1. We don't know how you figure its 1st day of pay period. It can almost certainly be done, some way.
2. What you wrote works, if you use the correct separator (;) and the Timestamp() function (and remove the extra ")")
I added the Let() to make it more readable (which I like to do).
t = Time ( Hour (Time_end); Int (( Minute (Time_end)/15 )) *15; 0);
Timestamp ( Date_end; t )
P.S. This is the 2nd time I tried to post this answer. The forum software is sometimes throwing me to a new (non-functional) page when I edit HTML, and the Back command did not work. I wish they'd fix this clunky Windows-derived forum; it's been a while.
Ok, I see how the Timestamp can clear up the merger query. Thanks.
Now, if I can find a chunk of code for calculating paydays, then I'll be set. I suspect one needs to know a seed date, say 8/16/2010, and then be able to find the closest Sunday that is a multiple of two weeks (60*60*24*7=604,800 minutes).