I think this is a bug.
Every time I open this It says a different time
#Time changes when I open this:
gilded mortar
pure vortex
I also reported this yesterday not sure what's going on.
worn mesa
The time to next level is a calculation based on your earning/s shown above.
Fluctuations in days to next level are a result of that number changing.
It takes a while to settle down, especially if it's the first time you've looked at the engine since collecting your offline earnings. This is the reason for any large fluctuation.