The new DHCP range takes affect at the next IP renewal, My max lease time is set for 15 minutes (because I knew I was going to be doing this change, and that makes it faster to apply for all clients).
The camera picks up a new IP in the new range just fine, I can tell my looking at the leases and checking for the MAC of the camera. The app just doesn’t update the info (or maybe the camera doesn’t send it, no idea which).
If you reboot a router, the devices will still happily keep their same IP lease until it’s half over when it will check in again to renew it, and depending on the router settings, it will keep the same one or get a new one. If you reboot the wireless, wireless devices will renew their lease when reconnecting. (my router and wifi are separate devices).