Summon Breaker VS Demise of the Land

If the turn player summons for a 3rd time, and to that summon's response window Demise of the Land is used, fetching Summon Breaker then Summon Breaker will not trigger and it will not be the End Phase of the turn.

This is because Summon Breaker needs to be face-up on the field at the moment when the 3rd summon happens, for its effect to trigger. If it arrives on the field after the 3rd summon then it missed its activation timing for that turn, and the turn player can keep summoning normally for his turn.