In recent years, laundry prewashes have switched from solvent-based products to enzyme-based products (in water).
This has some interesting implications. Firstly, it means that the prewash need not be applied immediately prior to washing. That is, it can be applied hours or days before washing. If the water evaporates, it doesn’t really matter, as the enzymes will stay behind and still do their job when the garment eventually is washed.
With the older style solvent-based prewashes however you couldn’t do this, as the solvent would evaporate and the effect of the solvent would be lost.
The other interesting implication of water based enzymatic cleaners use that day can be used for things other than clothes, such as spot cleaning of fabric chairs, car seats, carpets, and so on.
All you would do is spray some on, leave it for a few hours, then come back with a damp sponge and swab the area clean. You may need to repeat it a few times, or maybe spray on a little more Preen.
But allow time for the chemical do the work – don’t expect it to work instantly.