It's not unlike coffee or tea in that regard. You want a temp around 92 - 96C (197.6 - 204.8F) for the amount of time the saffron has in contact with the water. Once you have the desired flavor strength, strain it and set it aside.
It's also very forgiving. If the water is hot enough to make a cup of tea or coffee, it's fine. Saffron won't get bitter unless you actually burn it, which you're not likely to do in water. It's a king of spices for a reason - it has a very unique flavor and it is extremely easy to work with.
The more color it takes on while steeping, the stronger the flavor. You might want a little, a lot, or somewhere in the middle. The real trick is knowing when to strain it and set it aside. Treat it like anything else that is cooking and pay attention to its progress. Saffron can easily overpower other flavors that you wanted to bring out in a dish, especially with seafood.
Sometimes, you might want to just dump the whole concentration in, saffron included - depending on how you're using it. You can also make a cup or two of it at a time and freeze / refrigerate it to save some time.