Originally Posted by Master_Shake

Without a written contract, your sublease will follow the default rules for the jurisdiction you are in. There are sometimes rules that designate when leases end or start, and your rights in such a situation.

Without knowing your jurisdiction I can offer you this: Without a contract, if she calls the police and claims you are trespassing you've got a 50/50 shot as to whether they will remove you from the premises, or just leave the two of you to work things out.

This will probably never be litigated because of the short time periods and small amounts involved. It's up to you if you want to stick around and cause trouble or leave early.

From a fairness viewpoint, I think you should be given until the 30th, because:

The terms were never spelt out in advance, the oral contract should be decided in favour of the consumer/subleasee, who is in less of a position of power than the leasor.

and

Rents are generally paid for an entire month regardless of the number of days in each month, from the first to the last day.

But fairness isn't going to matter as much as what you can work out with your roomates. Perhaps you could offer to move out your belongings by the 25th, but be allowed to sleep on the couch for the last 5 days so as to avoid the commute.