Dealing with time format as string

Hi Guys,

I'm using  seconds counter then save those seconds in a field defined as string where eg. I do :

S time=30  

S time = $zt(time,1)  

Update myclass se timeSpent = :time

which now shows up as 00:00:30 if I do an sql query which good but the problem if I run a query to get average timeSpent I get 00:00.

having the field defined as integer would allow selecting avg but running a query in my Zen page wouldn’t show me a time format

so how can I get an average on my a filed defined as string in a sql query?

thanks