While more time to organize things sounds good, I hope we are aware of a couple of date/near/far effects:
1. The farther the date is, the less are the chances of enthused people getting involved right now.
2. You might want to consider 2 days of event, than a single one. You get more participation that way -- people slightly far away from the city/venue might be inclined to travel if they see more than a single day where they can contribute and get value-add in terms of plans, thoughts, and action. Secondly, topics discussed on day 1 give people a chance to regroup and come back the next day with fresh ideas. April 11 sounds okay. How about April 11 and 12?
3. Frequent change of dates may put participants off. Would recommend finalizing date(s) and sticking to them, no matter what.
Best,
Manish