My TWOC was 6 weeks ago and the process was:
Enure fully hydrated day before
Arrive at 08.30 at hospital for appointment. Urology department was super busy
Attended to at 10.00 - nurse explained what she was going to do. I was dreading the removal but it was OK with a few drops of blood.
Given a pad to wear and a piece of paper to record amount I drank plus a container for the urine.
Spent 1 hour reading my magazine and having some water until I needed to go. Urinated into the container and handed over. Container was checked (some blood as expected).
Nurse scanned my bladder to make sure that it was empty. All good and I was given some literature to read and all done.
Journey home was via taxi so I had a waterproof cover for the seat but no accidents en-route.
Some minor blood in urine for maybe 2 days after TWOC.
I have been very fortunate in that my continence has been good (8 weeks after op now and no pads at all). This was my biggest fear about the op.
Hope TWOC goes well and above detail will help reassure you.