Does a Painting Say 'Ding' When it's Done?

I've been painting this straight (kind of realistic) and have let this artwork sit for a couple of days.

My Mom and Dad's dog is in the background, with our Penelope dog in the foreground. The treat has not yet been visually revealed to them yet the scent has their complete attention.

These two are mature lady dachshunds who excel in the doggie-art of sleeping, cuddling and eating.  Now the promise of food is all there is.

Now I'm back at it, painting away on The Treat. Here is the work in progress:

The Treat (Work in Progress) by Laura Hoffman

This will evolve, this is just how the painting looks right now.

My ever present question remains: When do you know this is done? When to stop "dipping the brush?"

Here is the sketch:

Clean Pencil Sketch for The Treat by Laura Hoffman

OK, back to it....