it looks like only time part is coming through; you did mention that everything looks correct until attempting to push value into interface form, which is normally able to handle both date and time, so did you use Time instead of Date/Time temporary field as source in that action? If you replace that mapping with constant (e. g. 2020-05-01 01:00:02) does it end up being correct in change form?
It is Date/Time field, I tested once again with value Start Date and Time: 2020-04-07 00:00:00 End Date and Time: 2020-04-08 00:00:00 but the value pushed for scheduled end date ="1970-01-01 01:33:40", for scheduled start date is took correct value. Issue occurs with end date only,
The temp field which I used is character, however I tried with date/time, same issue happens with that datatype as well.
I assume your description stems from feeding your parser with mentioned data and observing workflow's behavior via logs; if you modify mapping for Scheduled End Date so that it becomes static (e. g. "2020-04-08 00:00:00") instead of variable (e. g. $temp End Date$), does value in Scheduled End Date still end up being beginning of epoch offset by some (possibly current) time? If it does, it probably gets mangled by workflow in destination form (normally, it would be possible that there is mismatch between format of source and destination value, but you've pretty much determined that it isn't in this case) so if you haven't already, trace what is going on with Scheduled End Date beyond Push Fields action you've been mentioning; if necessary, insert Message action at the beginning of modify (filter) workflow on destination form to verify value of Scheduled End Date received from Push Fields action.