I just read Article 50. The 2 year time period is not obligatory. The article just specifies that exit will occur after 2 years. Looks to me like the Brits could bug sooner rather than later. So why bug later, eh?
Because there are issues that need to be worked out. All the trade arrangements they hold within the EU could be overturned if they just bolted without negotiation, for example. What happens to British firms that have holdings in EU regions? What about the reverse, EU banks or financial institutions with major centers in London? British expats living in, say, Spain, what happens to them? Et cetera.
They need to work this out and the EU is going to go out of their way to make it extra painful. But if they simply walk out it would be more so.
Back two months ago, I was reading a piece which noted that the EU had decided that their whole way ahead on this negotiation episode...would be totally in French. Nobody from May’s team has said much but I would assume that there’s not going to be much serious talk, and the Brits will just stand up one day and say they are finished...with no final agreement.