In the northern half of the US anyway. Definitely, before any green emerges because the roots are already growing and hungry for weeks before any green shows.
I fertilized our garden beds last week. It will take some rain to sink it in. A good time to put down crabgrass preventer, and fert your nice lawns too.
I spread Preen at the same time in the flower and shrub borders. It works, sort-of.