I have set up a reminder on a task for 6 am but in the task list it shows as 11:59 pm.
Task list shows: Feb 1 2014 @ 11:59pm
Gray drop down shows: every 91 days starting 1 feb @ 6:00 am
When you enter both TIME and DATE in the Reminder dialogue, with or without recurrence, the syntax must be [TIME DATE] without recurrence or [every PERIOD at TIME starting DATE]. For your example, the syntax would be [every 91 days at 06:00 starting 01 feb].