I call the window between snow melt and bugs "secret season."
Sometimes it doesn't exist, as you point out. In other years, it's very long. There was a season about twelve years ago where we had fluke hot weather (80F for four days in early March). All the snow was gone by mid-March, and the bugs still didn't come out until mid-May, so we had a 2 month secret season.
I love secret season. No snow, no leaves, no bugs. It's good for rock climbing, and very good for scouting new climbs.