Is To Date required? How to set predetermined length.

Hello,

I would like to create a bucket item with a predetermined checkout time which can not be extended.

From /node/add/merci-reservation I would like the user to set a checkout date and time (From date) and then automagically add 60 minutes to it (rather than exposing the To date for the user to complete).

In my case, all reservations will be the same length. One use case would be to assist the assigning of BOF rooms. Anyone can reserve; no one can extend. Is this easily achievable?

Thanks!

PS: I'm running MERCI 6.x-2.0-beta11, MERCI Calendar View, MERCI Email, MERCI Permissions, MERCI Role Rule Override, MERCI Staff and MERCI UI in a standard Drupal install.