It appears that moodle enrollment time is somehow off. We are in UTC-8 timezone (America/Los_Angeles). When we enroll a student after 4 pm local time or so (about when the date change occur in the GMT zone) then the student enrollment starts on the next day at 12 am. The result is that the student can't login until several hours later. This is a real nuisance when updating class lists: students that are enrolled suddenly can't login until after midnight. I have reproduced this issue on 3 different systems. It occurs on an out-of-the box moodle setup with the defaults: timezone="Server's local time", and forcetimezone="Users can choose their own timezone." No special configuration in needed.

Please see attached screen shot, and note the local date/time in the upper right hand corner.

To reproduce the problem, click "Participants" in a course and manually enroll a student. Click the "Enrollment Options," one of which is "Starting from" which says "Today" and then lists tomorrow's date in parenthesis. As I said above, this occurs after about 4 pm in the afternoon when the date changes in the UTC/GMT timezone. It should say "Today" and then lists today's date in parenthesis.