May 8 is actually a Tuesday, if that helps; 10:30 AM is a brutal time for nearly everyone on a weekday. There's no one time that's going to please everyone, unfortunately; I have one on May 7 that I will also probably miss unless I can get someone to do it on my behalf.
It would be nice for Niantic to build in some flexibility into the EX system, such as having the invitation be valid at any Mewtwo raid within a certain radius of the gym you got invited to and informing you where they are times/places of all of them are.
