I start adding more waterings once we get to the 80s. I only water every hour if we are in the mid to high 90s or 100s. Last year we barely reached 100F for like a couple days I think.
You wont really have issues keeping the growing medium wet until the roots fill out the container, then it will basically be hard to keep them watered.
If you are using trays for them then its easy to tell when you need to water 
. I used to walk by and lift the smaller pots or tilt them over to see if they were dry or not. You get a feel for how fast the the plants can use up the water. If your saucers are still full, then I wouldn’t run them more either.