TogsTeam -
Everywhere else in Method we constantly doing time zone conversions - but there's actually no time zone conversion on that field.
What happens is that it syncs a changes-only sync every 20 minutes (by default). The next sync after your scheduled time is when your full sync will kick in.
So, say the changes only sync completes at 5:58 pm, your changes only syncs are every 20 minutes, and your scheduled full sync is at 6:00 PM. The next sync is 20 minutes from 5:58 pm, so it will be about 6:18 pm. At this point, since it is the first sync after 6pm it will do the full sync then.
The scheduled full sync is supposed to go off in the middle of the night, and the scheduled time is an approximation rather than an exact time.
I hope that sheds more light on it,
Paul