A bank can start foreclosure processes on your house once you have missed a payment,
and have exceed that grace period.
With that being said,
most banks will attempt to contact you and try to work out a repayment plan that will reasonable for both parties.
This time frame can vary from 2 months to well over 18 months.
If you are not going to pay,
I would recommend that you get in touch with your lender,
and at least attempt a good faith meeting to try to negotiate a lower rate,
or feasible repayment plan.