I had considered trying to let Sybase handle all the time-stuff

Personally that's what I might do, using the T-SQL dateadd() call, something like

select ... from ...
where the_date between dateadd(ss, -$seconds, $start_date)
  and dateadd(ss, $seconds, $end_date)
[download]

(using placeholders of course, $var used here for illustration purposes)

But then I'm really a database developer writing tons of SQL, these days... :-)

Michael