The water in the pipes is still cold. Tankless heaters are endless, not instant. You still have to wait until the cold water is pushed out of the pipes, same as with a tank. Tankless heaters are still installed in the same central location as a tank and the hot water has to come from that point.
Carcel
This is how they work and it's the best way to kill a necromancer. If you walk into a room and see a necromancer, count the number of steps it will take them to reach the door, back out and wait, step back into the door when they should be right on the other side. When they start summoning back out and they follow you into the doorway. The minion will spawn on the other side and you can kill the necro with no danger. You need to make sure the skeleton can see you through the doorway or it will wander off and the necro will resummon it on your side of the door.
This won't work if the necromancer is in a hallway and there is only one space free inside the door. The necro will summon on your side of the door in that case.
The reason this works is because the necromancer prioritizes buffing its minion over movement but only after the minion finishes spawning. So you can strategically place the necromancer in the minion's path before it finishes spawning because it will follow you for that one turn that it takes the minion to spawn.
The law requires public domain for US Government works. https://en.m.wikipedia.org/wiki/Copyright_status_of_works_by_the_federal_government_of_the_United_States
Most houses have a line going from the heater to the tap, not a loop, so the water just sits in the pipe waiting for pressure behind it to push it out of the tap. The cold water in the pipes can't be recirculated. I suppose you could plumb a loop through the whole house and constantly rerun the cooling water through the heater but that kind of defeats the energy savings from a tankless heater. That loop becomes a really long skinny tank that's right next to all of your taps.