Never. You will be paying for the rest of your life. Muahahaha. If you don't want to pay Mello Roos move to Santa Ana or Costa Mesa or some other Latino named city. Mello Roos keeps the riff raff out.
Based on the relevant CFD/AD. All houses in a given CFD/AD will have same terms unless someone prepaid. The actual amounts may differ based on apportionment.