I'm cleaning out my inbox and see this never got answered.
While MC provides a means to convert from internal date formats, it does not provide a means to convert back to internal format from specified date components. And this is non-trivial for a user to perform, due to varying number of days in a month, leap years, and other internal MC-specific implementations. It can be done approximately, but there will be round-off error with seconds.
For example, setting a date to exactly:
2009/02/26 12am yields a raw date of 39870.0000023148168111.
Using a math formula to convert hours, minutes, and seconds into a floating point time value, and adding your time specification of 19 hours, 0 minutes and 42 seconds, we have:
math([date, 0] + (19 + (0 / 60) + (42 / 3600 )) / 24 )
and the formatted date then becomes 2009/02/26 7:01pm, which has rounded and truncated your seconds value.
The floating point of the calculated value is:
39870.79296875
but we want
39870.7921527777798474.
for a difference of
0.0008159722201526 (about 70.5 seconds).
What would be required is a function which accepted as arguments standard textual representations of date components and translated those into an internal representation of a date.
Sorry for the delay.