It varies.
You can't really tell in advance what a ceremony is gonna looks like.
Sometimes, 30 min to an hour. Uncertainty in ceremonies are also factors not to neglect.
It may 10:45 , but start few minutes later.
Also,You will not be relaxed during the ceremony if you have an appointment in lesser than two hours time.
Why not try to book an appointment the next day after the oath ceremony considering the fact that no one can really predict.
Thanks.