If you want to keep an app on-screen on your apple watch you can take over control of that!

Go to Settings -> General -> Return to Clock

Here you may choose from:

  • Always - returns the moment you put your wrist down.
  • After 2 minutes - timed.
  • After 1 hour - timed.

I have found setting my watch to "After 1 hour" to be the most useful because that gives me manual control of when my watch changes focus.

To return to your watch face at any time, just press in on the crown.