Cats need to be trapped the day prior to surgery and stowed in a safe and secure place (in the traps) the night before surgery and the night post surgery.  Some clients do not have a garage or other secure place to keep them.  Ideally the overnighter would collect the trapped cats from the client the day before surgery and bring them to designated location early  the morning of surgery  and/or pick up cats following surgery in the afternoon for transport,  stow then for the recovery period, then return them to the client the next day for release.