I have three revolvers, with laser sights, and have struggled a bit, deciding what distance to sight them in. Two of them are 4"+ barrel .357 Mags, one is a 642.
I decided that I would not be using the 642, at 25 yards, or anywhere considered long range, so that gun is sighted at 5 yards.
The mags are sighted at 20 yards.
Arbitrary, I know, but you have to make a choice somewhere.
In daylight your lucky to see it at 10 yards, clothing can effect visibility as well but as you'll find out you won't hold still so the red dot will be moving around.
Red lasers are great in low light, but not much good in daytime. Green lasers are a lot better in daylight, but use up a lot more battery power. If buying new, I would go with green. As it is, I keep fresh batteries in the red ones I already have to make them as bright as possible.
I align my CT Laser sights so that the top half of the red dot sits directly on top of my front sight with the front and rear sight properly aligned at my desired aiming point at 15 yards. With that setting, I can still see the red dot behind my front sight at closer ranges and I can get good hits on the target out to 25 yards, which is likely further than I would ever be shooting at anything or anyone after dark. And this setting still works well for me inside my home at night.
Where I used to live out in the country, there was an electric utility line that was on my side of the section line road that passed by my home. Standing slightly off line with this pole line, I could easily spot my red dot displayed on the fourth pole away from me down the line after dark. Those poles were set about 300 feet apart, so figure that fourth pole was about a quarter mile away from me. You can see the red dot much farther away than you will ever or should ever be shooting, especially after dark.
My CT laser sights do NOT take the place of my gun sights. But they are an excellent accessory for my gun sights in low light or very little light after the sun goes down. This includes inside a darkened room or building during daylight hours when seeing sights properly is difficult. I know my bullets are going to land very close to where that red dot is showing. That gives me confidence that I'm not going to shoot something or some one that I do not wish to hit. BTW, I do NOT shoot at targets which I have have not properly identified! I also carry a good flashlight!