Purchasing Oyster Cards?

Probably not. Thats roughly the time when Public Transport re-starts again for the day. Most people who commute at that time already have Oyster Cards, so they dont tend to open the Ticket Offices. You'll probably have to wait around until about 6am. When you buy an Oyster Card, it costs �3 or �5 I think. You'll need at least �3 for your journey into London too.