I'll preorder online as soon as available and then try to book a slot in store to try them on, as I work 5 mins walking from Regent Street's one and 10 from Covent Garden 
If they are 100% sure that I'll be able to pick up in store on the 24th I might cancel the online order and do a new one in store
If they are 100% sure that I'll be able to pick up in store on the 24th I might cancel the online order and do a new one in store