I have been a schlub before, I know what that feels like. It is always self-inflicted. Yes, temps in the upper 90's after a "more is better" application of Weed B Gon on cool-season turf will not only turn your turf into toast, it will turn you into a schlub. And more is better? Lol...how did that turn out for you? Been there, done that. Anyway, I'm not advising this, but if you want to try it, spot spray the weeds with WBG at the label rate. If you get any on your grass, and you probably will, expect to see the same results from 2 years ago on any grass that gets hit with the herbicide. Maybe you'll get lucky with a timely shot of cooler weather. Do not water for 24 hours after the application if you want it to be fully effective. If possible, apply early in the morning.

One of the features of a plant that makes it a weed is the ability to bounce back from adversity faster than competing species. The same goes with garden insect pests. Aphids are born pregnant and will drop eggs about a week after birth. Lady bugs take months to go through a cycle like that. So if you spray an insecticide that kills both the aphids and the ladybugs, you will get the aphids back quickly. You will not get the ladybugs back until the population of ladybug food (aphids) is sufficient to support their return.

I have two thoughts on this. The first is that in general, it's better to apply fertilizer and weed killer separately. They sell them in one product for marketing purposes and ease of use, but if you fertilize first, the weeds start growing actively, so when you hit them with the weed killer a week or so later, it's more effective. The second thing is that you should wait until you've mowed the grass three times before using any weed killer n the lawn.

It's called fallowing, and it's done just the way you described. Water shallow and often as if you were trying to raise grass seed. Then whack it with RoundUp. It's not on the bottle, but it's safe to put down grass seed a few hours after the RoundUp is dry. After the grass seed establishes, move to deep/infrequent watering - that will make the grass healthier and will avoid a lot of weed sprouting.