I use the Choice activity (showing the names who have selected each option) to allow people to choose all possible times that people can attend a chat session. People can update their choices as the time gets closer and people are encoraged to swam into the more pupular sessions. This works best if people specfy all the possible times they can select. Currently the workaround it to give people the followign selections

Mon 9am | Tues@11am | Wed@5pm | any session | Mon or Tues | Tues or Wed | Mon or Wed | I can't attend any session

It would be much easier if i could offer the following option

Check all the sessions you can attend:
Mon 9am | Tues@11am | Wed@5pm | I can't attend any session