I typically stop running (or at least training) in the winter. And start again early March. I'm normally back to my best by July, so 3 months sounds about right.

This is only for short stuff of course. Endurance training takes longer to build.

You could argue I'm always building on last year's gains. That's probably right for muscle conditioning and tendon strength and all that long-term soft tissue stuff. We're just talking about fitness here.