Play time does not display correctly under Play Activity within your user page.
A software title you have played for several hours now displays as being played for a shorter amount of time.
Note: If you have used your Nintendo Account to play the same game on more than one Nintendo Switch console, your play activity may not reflect your total time between all consoles.
What to do
Update your console to the latest version.
Continue playing to see if the time played listed under Play Activity begins to increase.