ANSWER: Home loan interest rates change on a daily basis. They can change more than once a day. When you get a quote, it becomes your rate once you lock-in with your selected lender. A lock in is a promise (in writing) to close your loan at a certain interest rate and points.
You should have a lock-in agreement with clearly defined terms. These terms include expiration date, interest rate, and points paid by buyer and seller, and they usually include the expectations you should have of your lender as well as those they have of you. Be sure you understand all of the rules involved.
It is important that you know about your lender's strength and reputation. The promise offered to you is made more valuable by these two. Once you read this disclosure carefully and agree to the conditions, be sure you have a fully accepted and executed copy for your files. This is your contract with your lender and protects your interest rate.