For Canadian cards: (and I can't imagine it being very different elsewhere, unless you paid extra premium for the coverage)

WHEN DOES COVERAGE BEGIN AND END?

Coverage ends on the earliest of:
1. midnight of your return date;
2. the date your card account is cancelled;
3. the date your card privileges are terminated;
4. the date the cardmember’s card account is no longer in good standing as per
the cardmember’sCardmemberAgreement issued byAmexBank ofCanada;
5. the date the group insurance policy terminates.