Here's a good starting point for guidelines:
Also check your county extension service's website. Pay attention to their watering recommmendations for your soils.
As for not applying fertilizer if it's hot . . . then when could we apply it?? (BTW, the record high at Austin-Bergstrom on February 21 is 101 set in 1996! YES, FEBRUARY 21!)
For southern turfgrasses, apply ferts when the lawn is actively growing.
You can apply Milorganite (or Houactinite- same thing, just from Houston's sewage system) any time. It won't burn. Other fertilizers, use common sense. Don't apply to a wet lawn. Water it in ASAP.
In the spring, apply fertilizers high in K to build deep strong roots. Build a thick dense turf, and you won't need much in the way of herbicides at all.