I didn't think about it when I installed it.
Was at 307 no long after I fired it up. Maybe 3-4 minutes.
My spa runs for an hour every morning. The heater warmed it quickly. When the pool was turned on after the spa, the heater warmed up the pool pretty fast as well. I set the pool pump to run 40 GPM instead of 30. That seemed to speed up the heating of the pool. I wish I had known that over the winter.
I live in Louisiana and keep my pool open year-round.