Thinking of migrating to Sky

Hi I'm currently with Bulldog ,which recently has been nothing but trouble for me (and expensive), and am considering moving to Sky.

I registered my interest a long time ago and have just recieved notification from Sky that they are ready to take orders at my exchange.

However this is going to be a problem in that with Bulldog I'm LLU so wont be able to just ask for a MAC code.

Am I right in thinking I will need to firstly ask BT for Return To Donor and then ask Sky to connect me? If thats the case what sort of timescale is it between the request and actuall connection as I'll be without any Broadband service at all for that time?