see this

https://community.intersystems.com/post/how-create-index-inside-array

it's easy, without AM/PM

write $tr("abcd-ef-gh ij:kl:00","abcdefghijkl",202010011000),! // ODBC-Format
write $tr("gh.ef.abcd ij:kl:00","abcdefghijkl",202010011000),! // German-Format
write $tr("ef/gh/abcd ij:kl:00","abcdefghijkl",202010011000),! // US-Format

but if you need AM/PM, then the shortest way is using $zd()/$zth() functions

set datetime=202010011000
set tmp=$tr("abcdefgh ij:kl:00","abcdefghijkl",datetime) // or using $e(...)
set tmp=$e(datetime,1,8)_" "_$e(datetime,9,10)_":"_$e(datetime,11,12)_":00" write $zdt($zdth(tmp,3),1,3)

To make your (and others) life easier... here is a simple class to display a dynamic object (or dynamic array).

/// A general class for various helper functions
/// 
Class %zapi.utils Extends %RegisteredObject
{ /// Show an dynamic array or object
/// 
/// obj : the dynamic object (or array) you want to display
/// deep: max path depth, 0 (default) = display all
/// find: if given, (a part of) a property name
ClassMethod ShowObj(obj, deep = 0, find = "")
 {
   new %seen
   do ..shObj(obj,deep-1,find,"<obj>")
 }
ClassMethod shObj(obj, deep, find, path) [ Internal, Private ]
 {
   set path=path_"."
   set itr=obj.%GetIterator()
   while itr.%GetNext(.prop,.val) {
      set:obj.%IsA("%DynamicArray") prop="%Get("_prop_")"
      set prop=path_prop
      if $isobject(val) {
         if $data(%seen(+val)) { set val="same as --> "_%seen(+val)
         } else { set %seen(+val)=prop }
      }
      if $isobject(val),deep { do ..shObj(val,deep-1,find,prop)
      } else { write:prop[find prop,": ",val,! }
   }
 }
}

With our old pData,  use it as follows:

write pData 
[{"patient":{"guid":"12345","id":12345,"forename":"Joe","surname":"Bloggs","dateOfBirth":"2002-12-10T00:00:00Z"},"visit":[{"guid":45678,"date":"2020-01-10","reason":"other"},{"guid":45679,"date":"2020-01-11","reason":"routine"}],"
documentAttachments":[{"guid":"23432","id":152,"catergory":"notes"},{"guid":"23433","id":153,"catergory":"summary"}]}]

set obj={}.%FromJSON(pData)
do ##class(%zapi.utils).ShowObj(obj)

If you don't want to write each time a novel, you can create your own "show object" command too.
Insert the following line into %ZLANGC00 routine (if %ZLANG doesn't exists, create it):

ZSHO(obj, deep=0, find="") Public { do ##class(%zapi.utils).ShowObj(obj,deep,find) }

and Voila!, you got a short command to display dynamic objects

zsho obj              // display the whole object
zsho obj:2            // display up to  second nesting level
zsho obj::"visit"     // display all occurrences of property visit
zsho obj::"guid"      // display all occurrences of property guid

The outputs of the above commands are

USER>zsho obj
<obj>.%Get(0).patient.guid: 12345
<obj>.%Get(0).patient.id: 12345
<obj>.%Get(0).patient.forename: Joe
<obj>.%Get(0).patient.surname: Bloggs
<obj>.%Get(0).patient.dateOfBirth: 2002-12-10T00:00:00Z
<obj>.%Get(0).visit.%Get(0).guid: 45678
<obj>.%Get(0).visit.%Get(0).date: 2020-01-10
<obj>.%Get(0).visit.%Get(0).reason: other
<obj>.%Get(0).visit.%Get(1).guid: 45679
<obj>.%Get(0).visit.%Get(1).date: 2020-01-11
<obj>.%Get(0).visit.%Get(1).reason: routine
<obj>.%Get(0).documentAttachments.%Get(0).guid: 23432
<obj>.%Get(0).documentAttachments.%Get(0).id: 152
<obj>.%Get(0).documentAttachments.%Get(0).catergory: notes
<obj>.%Get(0).documentAttachments.%Get(1).guid: 23433
<obj>.%Get(0).documentAttachments.%Get(1).id: 153
<obj>.%Get(0).documentAttachments.%Get(1).catergory: summary

USER>zsho obj:2
<obj>.%Get(0).patient: 11@%Library.DynamicObject
<obj>.%Get(0).visit: 2@%Library.DynamicArray
<obj>.%Get(0).documentAttachments: 21@%Library.DynamicArray

USER>zsho obj::"visit"
<obj>.%Get(0).visit.%Get(0).guid: 45678
<obj>.%Get(0).visit.%Get(0).date: 2020-01-10
<obj>.%Get(0).visit.%Get(0).reason: other
<obj>.%Get(0).visit.%Get(1).guid: 45679
<obj>.%Get(0).visit.%Get(1).date: 2020-01-11
<obj>.%Get(0).visit.%Get(1).reason: routine

USER>zsho obj::"guid"
<obj>.%Get(0).patient.guid: 12345
<obj>.%Get(0).visit.%Get(0).guid: 45678
<obj>.%Get(0).visit.%Get(1).guid: 45679
<obj>.%Get(0).documentAttachments.%Get(0).guid: 23432
<obj>.%Get(0).documentAttachments.%Get(1).guid: 23433 

Have a nice day...

The above should work, so the question is, what is the content of pData. Do you can share a sample with us?

Also, you can write the above somewhat shorter too and you can access all the properties either via propertyname or via the %Get() method.

I assume, you have a string like this:

set pData="{""Name"":""Joe"", ""Age"":50}"

the you can do this

set object={}.%FromJSON(pData)
write object.Name // Joe
write object.%Get("Name") // Joe
write pData // {"Name":"Joe", "Age":50}

Now we have the year 2020 (but I will discard this year from my life because of Covid-19) but our loved COS wasn't in this year nor in  the very past years invented.

COS (better, the predecessor, M ) has more then 50 years under his belt, it was created in the late sixties - in a time, where RAM was rare, expensive and therefore it was measured in units of kilobyte!

If I recall correctly, at end of the seventies, we had some customers on a PDP-11/34 with less then 64KB of memory, one or two 2kb partitions and some "big" partitions with 4KB or 6KB, the rest was for disk buffers (512 byte each) and DEC's V4b (which acted as OS, database and language interpreter).

Hence the ability of COS for excessive abbreviations and if you get an old routine, written by an old school programmer (like me) then you will see there (mostly) abbreviated commands,  postconditions and (local-/globalvariable, label and routine) names, consisting just a few letters (one to three, maybe four).

Unfortunately, this (abbreviated commands, short names) happens to me in this days too - you know, old habits never die.

There is a wonderful (and at the same time a horrific) example of such a routine: one letter names, everything abbreviated:
https://stackoverflow.com/questions/4151554/need-mumps-sample-code/4430…

clock ;; a digital clock from
;; https://stackoverflow.com/questions/4151554/need-mumps-sample-code/4430996
;;
Q N R,Q,C,D,E,W,B,G,H,S,T,U,V,F,L,P,N,J,A S N=$G(N),Q='N,F=Q+Q,P=F+F,W=$L($T(Q))
 S W=$E(W,Q),S='N_+N,W=W-F*S,L=$G(L),R=$C(Q_F_P),R(F)=$C(F+Q_F),R(P)=$C(W-F) W #
 S T=$E($T(Q+F),F,W\S)_$C(W+S+F) X T S B=$P(T,$C(P_P),F),C=B\(W*W),D=B-(C*W*W)\W
 F G=S-Q:F:S+F+Q S E=B-(C*W*W+(D*W)),H=$E($T(Q),G),@H=$S(@H<S:'Q,Q:N)_@H,T=C_D_E
 F A=Q:Q:W\S S J=$E(T,A),C(F)=$S(J>(F+Q)&(J<(S-F)):Q,Q:+N),C(P)=$S(J#F:Q,Q:+N) D
 .S C(Q)=$S(J<(S-F):+N,Q:Q),C(F+Q)=$S(J>Q&(J<(S-F))&(J'=(P+'L))&(J'=(P)):Q,Q:+N)
 .S H('L)=L F  S H(N?.E)=$O(C(H('$G(N)))) Q:H('+L)=L  S F(A,H('L))=C(H(W[(W\S)))
 F U=Q:Q:P W !,R F V=Q:Q:P+F W $S(F(V,U):'Q,Q:$C(P_(W\S))) W:'(V#F) $C('N_F_F+F)
 W !!,R(F)_C_R(P)_D_R(P)_E_R(F) X $RE($E($T(Q),Q+F,P+Q))_R(P)_'N W # G:N=L Q+F Q

It's not only tricky to read but has an attractive form too

ISO 8601 time format is either yyyy-mm-ddZhh:mm:ss (UTC time) or yyyy-mm-ddThh:mm:ss+TZ (local time)
where TZ is the time zone.

If both times are UTC time, then just compare.
If the times are local times and both times are in the same TZ then just compare
in elsecase either convert both times to UTC or one of the times to the TZ of the another time.
Then just compare.

The compare function is just a $select(), nothing more:

t1, t2 are the times, then

if $select(t1]t2:"t1 later", t1=t2:"equal", 1:"t1 is earlier")

or more general:

set result=$select(t1]t2:1, t1=t2:0, 1:-1)
if result>0 write "t1 is later then t2"
if result>=0 write "t1 is later or equal to t2"
...

If the class is in use (i.e. instantiated) then it will use the "old version".
So you have to take whatever  step(s) needed (stop production, stop Cache/IRIS) to unload the old version.

After more than 42 years of M-programming and in total of 48 years of programming experience I would say, if you need a class with about 1000 or more properties than something is wrong with your (database) design. There is nothing more to say. Period.

Maybe you want to use TO_DATE(...)  but if you want to use TO_CHAR() then you have to supply a correct argument, which is in this case a $HOROLOG value

SELECT TO_CHAR(0,'mm/dd/yyyy') ---01/12/1840

SELECT TO_CHAR(65575,'mm/dd/yyyy') ---15/07/2020

TO_CHAR(): A string function that converts a date, timestamp, or number to a formatted character string.

TO_DATE(): A date function that converts a formatted string to a date.

Oh yes, back in the seventies (and later), "X ^%" was our daily bread...

This should be something like:

do httpRequest.EntityBody.Clear()

do httpRequest.EntityBody.Write("Your Data")

set status=do httpRequest.Post(...)

If I understand you correctly,  you want something like

select * from yourTablename where yourColumname %PATTERN '1.N'

i.e. where a column contains an integer greater or equal 0 (1.N means: one or more digits)