So long as your table companions don't want to talk too long you shouldn't miss any of the shows. In my opinion Concierge Class is worth it but it really depends on yourself as to whether you consider you get value for money and on this occasion you will be able to try it out. I'm sure you'll have a great cruise on Constellation ... Neil.
Normally there are two shows the timings can vary sometimes the 2nd sitting show is at 7 and sometime 10.30, but no you should see all the show before you go for 2nd sitting at 8.30, doors don't close until 9
On Consierge we have used it now on 5 cruises and we like it, breakfast in the stateroom when we want it pastries at 5 p.m. and left if you are not there plus some gifts priority boarding and a few others. We have also tried a suite and I think personally Consierge is better value. The way Celebrity count points for their Captains' club membership is on a 10/12 day cruise 1 point but with Consierge you count 2 so a bonus there, if the cruise is over 12 days you count 3 and the more poiunt you get ..... Enjoy your cruise and write a review when you get home.
You will not miss the shows. They are timed to be either before or after dinner. On Century they sometimes started at 10.45, and dinner was at 8.30.