Do I schedule a time with them or can I

Definitely schedule especially if your car takes an odd size or has special needs. They can't possibly keep everything in stock for every car, so the need for an appointment goes up proportionally with the rarity of your vehicle :)

I'd recommend a scheduled appointment, but they take walk-ins. Best to get there right when they open.

Do schedule a time. They are busy

They're pretty good about working you in, but they're busy and it's first come first serve. If you already know what tire(s) -- brand, style, size, etc. you may want to call to make sure they have sufficient inventory on-hand.

They'll take drop-ins and won't leave until the last car is done, even if it means staying well pass their business hours. Best to book an appointment if you don't want to wait for a long time. I waited for 8 hours and didn't know when it was going to be ready.

You can try and schedule an appointment but they are very busy

Better to schedule an appointment with them if you need tires mounted and installed in a certain time frame. You can however just show up and they'll put you in next available slot.