In an emergency I've mixed and used it inside of five min's. Most of the time it's more then a week. I have two 35 gallonish rubbermaid cans, one for RO and one for Saltwater. I have a 900gph pump running continuously on the salt side to keep it mixed. I've never heated the water.

I mix my salt until it is all dissolved, < 5 min, using tank temperature water and pump it in as I siphon detritus and old water out. Been doing that for years. Change 10% water every week. Fish and corals are in excellent condition.

about 10 - 15 min, as soon as I can see clear to the bottom of the bucket, it goes in the tank

Anywhere from when it's clear (after adjusting for salinity) to a couple days ahead... If too much water evaporates from my mixing bucket (I try to avoid this anyhow, distilled water isn't cheap) there is a white deposit left on the pump and bucket since I dose the freshly mixed water with calcium and magnesium while it's mixing. The pump heats the water to a reasonable temperature also, so I don't use a heater.

Usually a day or two, although instructions usually say that it can be used immediately (but reccommend aerating until O2/CO2 equilibrium is met) not sure how I would measure that.

Voted 2 days but usually now plan for a week (a couple of days the fresh ro/di aerating, then few more with the salt). In the old place with FOWLR, used tap water and de-chlorinator in a bucket in front of the tank and as soon as I dissolved the salt, mixing with my hand, had a water change going.

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I voted a couple of hours just because it was the shortest time increment. I'm with Christy, I usually mix it for as long as it takes for the water to clear. Which is usually the time it takes me to do all of my other water change tasks. I'm kind of bad with the heat thing though. I don't heat it up as I usually have it stored in jugs at room temp. It does lower my tank temp a couple of degrees but nothing bad has ever really happened while doing it this way. The way I see it cool and warm currents move through reefs all the time, changing the temperature for a while. So in a way, I feel like I'm copying a natural occurance.

I didn't vote, the salt can be mixing anywhere from 5 min to 2 months

Always 3 days,just what i've done.

Sounds like it doesn't matter a ton either way....