It's my mainphase and I decide to cast Damnation. My adversary in response... cast Boromir, Warden of the Tower whit Hideway mecchanics of a land (which allows time restrictions actions), and then sacrifices it to give indistructible to other creatures.
If the casting was legal then there would be no problem Boromir doesn't have any restriction on its sacrifice ability. So whether via a Hideaway mechanic or simply giving it flash via a Vedalken Orrery or similar card. Once Boromir is on the battlefield, unless some other card restricts the use of his ability he can sacrifice the same turn he enters play.