Short answer... about 30 minutes.
I had tubes put into both ears about 3 weeks ago and showed up to the clinic an hour early (6am) and then had my appt at 7am. By 7am I was in a gown and ready to rock and roll. I went in... had local (next time I'd go general and have them knock me out) which means an injection into the ear for numbing. (hurts like heckers)
Then I got about 10 minutes per ear of really bad white noise/static. Not uncomfortable - just odd. Following both ears I walked (like a drunken woman) back to the chair for recovery with a LOT of help from the nurse. I promptly then got ill thanks to the dizziness and was asked to stay until I felt better. It wasn't until approx 9:30am that I had my husband come and pick me up. (Leaving my car in the parking lot that they had said I would be able to drive home no problem).
I went straight to bed and woke up around 2pm with the dizzy feeling mostly gone. It has been just over 3 weeks now and I still feel like I am on an airplane with the muffled sounds and hearing my own voice is still - odd and unsettling. It's really effected my anxiety level, sadly.
So, in the end - it's a short, easy procedure (for most, I think). But I would be ready to have someone drive you home.
Hope you have a better experience.
I've heard from many others that it was a piece of cake for them. Not sure why mine had to be so icky.