Yes, 24-hrs is the typical minimum. And yes, I'd want the water level just below the height of the curb, so fill the pan.

The following is technique. Not required.

If you just marked the water height on the edge of the pan's curb and came back a couple of days later and the water
level dropped, the water level might have dropped due to a leak, or it
might have dropped to evaporation. Or both.

I set a plastic container upside-down on the pan, usually near the drain, so it acts as a cup and will hold water. I shim as needed to make sure the top of the container is level. The top rim of the container needs to be lower than the height of the pan's curb. It's weighted so it doesn't float. Let's say that container is 2" tall. I'll fill the pan with water until water overflows from the pan into the inverted container, filling the container to the rim. I stop when the container is full to the rim. The water level in the pan as a whole should be right at the top of the container's rim, so the level of water in the container is the same as the level of water in the pan. I hope that makes sense.

Evaporation losses will be pretty much equal in the container and in the shower pan. So if you come back in a few days and the water level in the container and in the pan have both dropped 1/8", you can think of that water loss as only being from evaporation.

If you come back in a few days and the water level in the container has dropped 1/8" but the water level in the pan has dropped 3/8", then you can figure that you have some evaporation loss (1/8") from both the pan and the container, but you also have water loss in the pan (1/4") due to a possible leak.

Even with water loss in the pan, the leak could be a no kidding true leak from a poor seal at the drain/pan flange, or it could be because the drain plug itself wasn't properly set in the drain hole. The plumber can investigate, if no evidence of a leak is found, the plug can be reset and another test performed.

The use of the container is not exact. It's just tool to help measure.

To add one extra point? Your swanstone pan is a solid surface, so the following will not be an issue. But let's say this was a Kerdi-lined pan. When you fill a Kerdi-lined pan with water, there can be some tiny air bubbles entrained in the fleece of the Kerdi fabric. Over time those bubbles can escape. With the bubbles gone, the fleece will be fully wet, and the water level could drop a tad, even with no leak. So each type of pan is different, and material differences need to be taken into consideration. With a Kerdi pan, once the fleece is saturated then the leak test can begin, because that's your true starting water level. That's being overly detail oriented, but hey. Sometimes on these forums we deal with real world, other times with theoretics.

To put the "slow leak" into perspective regarding how much the water level in the pan could drop due to a leak?

If your shower pan is 4' square and you filled it with water, if a slow leak resulted in a loss of one gallon of water, the water level would drop about one-tenth of an inch due to the leak.

Hope this helps more than it confuses.