Hmm, I think you've got a pretty good balance there. :)
Ofcourse there's always a danger with specifying anything that may yet change. There will always be somebody who complains if it doesn't go exactly as you announced. You may need a permanent "Disclaimer: this is an estimate, events may change considerably based on player actions during the event" after your specifications :P
But I see a lot of disappointment now when players' expectations that they based their decision to attend or not on turn out to be completely wrong, both when they attend an event they didn't want to be at and when they miss an event they did want to be at. So I think the pros would outweigh the cons in this case. I say give it a shot.
Ofcourse there's always a danger with specifying anything that may yet change. There will always be somebody who complains if it doesn't go exactly as you announced. You may need a permanent "Disclaimer: this is an estimate, events may change considerably based on player actions during the event" after your specifications :P
But I see a lot of disappointment now when players' expectations that they based their decision to attend or not on turn out to be completely wrong, both when they attend an event they didn't want to be at and when they miss an event they did want to be at. So I think the pros would outweigh the cons in this case. I say give it a shot.