1) When you create a webinar and set a time we store in UTC format with an offset of your timezone.
2) When a student sees the time - we convert it to their timezone.
For example, if you create a webinar starting at 11:00 in the morning (while keeping timezone in Chicago = UTC-6:00), a person in Helsinki (UTC+2:00) will see start time at 3:00 in the morning (since there is 8 hours difference between cities).
As long as you and your student's set timezone corresponding to their current location - there is nothing to worry about.
If you want to change timezone please follow guide How to change a timezone.