For projects where a Warranty period is sold, the customer can benefit from bug fixing even after the application is accepted or project goes live - what occurs first - and the team dismissed. The Warranty effort is different from other project items: this effort is an insurance to cover application errors and in an ideal scenario it won't be spent at all. If you are spending more something went wrong with your project and you’re having quality issues. Usually this is an one month period, but can be extended or reduced in the sales cycle, so confirm what was agreed on the proposal.
Team, and specially the Engagement Manager, should do all efforts during the project to prevent spending this warranty, namely through effective quality process.