This depends on the length of your deferred period. You choose this when you set up your policy. You can claim as soon as your policy is active, however, you won’t receive any benefit payments until the deferred period has passed.
Insurers commonly offer deferred periods of 4, 8, 13, 26, and 52 weeks. You can have a 1 day deferred period. So, if you choose an 8-week period, you will have to wait 8 weeks to start receiving any payment from your policy after a claim.