Is there a license contract or time period?

In this article:

Phone number licenses are month to month with the agreement renewing monthly until the licensee cancels the number in their account or is delinquent on their bill. There is no contract to sign or a minimum or maximum license time requirement.

You may also want to check out the following articles for more information about licensing numbers:

Can I cancel a licensed number?

How does licensing a phone number work?