In interop Ens.MessageHeader, we have TimeCreated and TimeProcessed. I would along the same lines and have TimeCreated and TimeUpdated. I find Time… more appropriate as those are time stamps, not dates.

Use the concatenation operator, _ (underscore) in the value of the assign action. Something like : source.{EVN:5.2}_source.{EVN:5.3}

You can achieve this by querying Ens.MessageHeader (see https://docs.intersystems.com/irislatest/csp/documatic/%25CSP.Documatic....).

something along the lines of

select top 1 TimeProcessed From Ens.MessageHeader where TargetConfigName='MyConfigItem' order by TimeProcessed desc