Wing it Like Witches takes place shortly after Understanding Willow. No more than a few days.

The key is Amity's hair. We know she dyes it green and that her brown roots are growing out over her forehead.

This is how Amity's hair appeared in Understanding Willow.

static.wikia.nocookie.net

This is how Amity's hair appeared in Wing it Like Witches.

static.wikia.nocookie.net

There's practically no change. Had weeks or months passed Amity's hair would either have a lot more brown in it or it would have been re-dyed back to completely green with a tiny bit of brown growing back. Her hair would not look exactly the same unless there was a very small passage of time between the two episodes.