Account migration complications?

I have found the steps to migrating my account for when I change my number but I would like to explain my situation fully so that I can be guaranteed I won't lose any chat history. I am moving from one mobile network service to another. Tomorrow, my current one will be cancelled so that I can no longer use it. I will be receiving a new number soon but it is hard to say exactly when. It does take time for it to activate. So here is what I would like to know. Can I use whatsapp between the time my current service is cancelled and when my new number is activated? When exactly should I go forward with migrating my account in WA settings?