There will generally be solid snow in southern CO until mid-June. Wolf Creek Pass is one of the snowiest areas in Colorado, so even in a low snow year, there will probably be some snow there until early June. Most thruhikers begin at the Mexican border in mid to late April. If you start much later, it can get very hot, and in a dry year the ranchers will turn off windmills etc. making it very hard for hikers to get water as there are few natural sources. In a very dry year, they will also close the forests in mid or late May. Starting much earlier can mean a lot of snow melt in the Gila, and snow in the far north of NM and, of course, Colorado.
Ginny