Really, spray whenever you want except when dealing with fertilizer.
Spray a good 7-10 days (minimum) before you put out any fertilizer. You want that clover to be good and dead before you fertilize or else parts of it will pull through.
Mixing with roundup is a good way to get grass/broad leaf coverage. Additionally, you will get better rain coverage. Generally, you want 12 hours (minimum) w/o rain with 2,4-D. Mixing with roundup can knock it down to 30 min.
Don't put roundup/2,4-D mix on your yard.
Be careful around ponds/creeks etc. 2,4-D isn't good for the fishies/amphibians. I know it's restricted use in some places.
This post was edited on 3/18 at 7:44 pm