How long does battery replacement at a Genius Bar take

It depends on how busy the store is, when you drop off the phone, etc.

When I had mine replaced earlier this year, I left my phone overnight. It was ready 3 hours after I dropped it off, but with the store being 20 minutes away, I just picked up the phone the next day.

Calling the store is your best option to get an answer here.

~Lyssa

Does the store have the battery in stock? If not, it might be 2-3 days.