Toontown opens one hour after official park opening. Those with Mickey's Toontown Morning Madness (only available through packages) can get in at official park opening. MTTMM is only on Monday, Wednesday, Friday, and Saturday.
So on a day where the park opens at 8 (I'm guessing a Friday or a Saturday), then MTTMM would be right as the park opens. Give the people who have MTTMM about 15 minutes to get back there, so the festivities start probably around 8:15. Then people with MTTMM will be the only people in Toontown until 9AM when it opens up to everyone.