Help - When to schedule a Webcast?

ACTE is scheduling a Webcast soon, and I'm trying to pick a time that would give classroom teachers the greatest chance to attend. I was thinking of 2:30 or 3pm ET/11:30 or noon PT as a time when East Coast teachers have just finished class and Pacific Coast and Mountain Time teachers may be at lunch. Unfortunately neither of those times are great for Central Time teachers.

Any feedback? I've heard that it's confusing to start a Webcast on the half-hour, but I'm not sure I agree with that.