Hey Frac, as you get a little more acclimated to the area, you will learn which parks do and do not drain well after a good rain. I will say, that as long as it is not a torrential downpour, Allaire is safe to ride, as long as you avoid the river trail, and the other few spots of the park that dont drain so well.
As for the TM starting so early, my guess would be to accommodate the ones with other family obligations, beating the hotter temps later in the day, giving enough time to do the required work with enough time to ride after the TM.