Most liquid Glyphosate products, including RoundUp QuikPRO, if kept at moderate temps in a cool dry place will have a shelf life of 3-5 years.
Roundup QuikPRO is rainfast in about 1 hour so watering the next morning after application is fine.
Roundup QuikPRO does come with a surfactant in the formulation. There is no need to add an additional surfactant.
If only a small area of the lawn is affected by the outbreak, spray only the affected area with RoundUp Quick Pro. If the problem amounts to no more than a few spears of quackgrass in an area of your lawn, paint the individual spears with diluted RoundUp QuickPro. Becareful to avoid getting the product on desirable grass. If most of the lawn has been affected by quackgrass, the only sure fire way to get rid of it is to spray the entire lawn with Roundup. Spray when the lawn is growing actively, preferably in the spring. The treatment will kill the lawn grass as well as the quackgrass. After about two weeks, you may begin the replanting.