When is the best time to spray ? Should I cut the grass first ? Morning / Night ?

I sprayed in mid morning and it was very effective. Knocked them down with no problem.

It's not necessary to cut your grass first, but you should avoid mowing for 24 hours after applying. It doesn't matter if you apply in the morning or evening, but to control surface insects, you should plan for enough time to water the area a few hours before treating.