Hi Gromit, the actual recording took about half an hour, however before recording there is an informal chat so the audience is at ease and able to enjoy the show. After the recording they chat and thank you for going and let you know when the show is going to be aired. All in all about an hour, good fun.
Went on Tuesday and it was excellent. They record 2 half hour episodes on one night. Each show took about 1 hour 15 minutes to record and they had a twenty minute interval. They had a bit at the end where Humf had to redo some lines that he'd fluffed.