Hi!
Unfortunately, there is no way to start all markets at a specific time of the day. This is the first time I hear of such need, but if other users back it, I'll add it to my to-do for future updates.
For now, I can just suggest starting all markets as early as possible, i.e. by setting "Start monitoring events at ... mins" (in Monitoring Options) to its maximum value of 1440 minutes (=24 hours).