Heat and sunlight.
As long as you use it within a couple of days you are good. I have a 50 gallon translucent tank and there has been SH in it for a week and I don't notice it getting weaker. I do notice if it is weak to begin with, as in a bad /weak batch. But if it is a fresh batch it lasts until it is gone. I've had jugs of SH in my garage for three weeks and it was still good. And it gets hot in my garage. If you are worried about sunlight, just get some colored containers.