Breaking a years lease; when must I vacate?

Essentially, if you are already late on rent, the landlord may begin eviction proceedings at any time. That's the bad news, as is the fact that eviction proceedings are fairly streamlined--only take a few weeks, usually.

The good news is, the only way to get you out legally is by the eviction processs--the landlord cannot simply change the locks, etc. So you have until they go through the process. You might want now to begin looking for alternate arrangements, to make sure you're not caught out when it happens.