John,
When your driving ban is over, you can fill out the application form for a new licence and send it to the DVLA with the appropriate fee to get your licence back. There's no such time limit as such but you will not be able to drive until you get your driving licence reinstated. Therefore it is advisable to request it sooner rather than latter as you never know when you will need to drive and having the licence back will come in real handy.
