Remember dandelions will be at their maximum yellow bloom about the date of the first mowing. Veronica also if you have it in your area. Chickweed and wild garlic also prominent. Violets, creeping charlie, and Oxalis appear a few weeks later--about when the temp first hits 80.
When the temps start hitting about 85 (if at all), then spurge, mallow, purslane, crabgrass and other summer annuals appear, (plus nutsedge).
When temps cool off in the fall--I estimate about highs of 65--then new dandelions, veronica, chickweed, henbit and the winter annuals appear.
I never did much spot spraying. It takes almost as much time as blanket spraying--and there is always the chance that you will not see small weeds, and thereby miss them.