If you already have the same service from Bell, then there shouldn't be any real work required to switch your line over physically. They would need to ship you a new modem (a couple days) and then you could probably be up and running right away.
If you don't have the service yet from Bell, then they'll need to send a Bell technician out to configure your line which I suspect would take a week or more. Best to call them to find out. Feel free to drop my name as your referral and they'll give me $10 off my next bill.
-Pete