Quick answer
What to do
Record your cash before leaving, return after a known interval, and compare the difference. Treat the result as a personal observation, not a universal formula.
1. Record a starting value
Write down the cash shown before you leave the experience.
2. Use a known interval
Return after a measured period without changing pets or upgrades during the test.
3. Recheck after updates
Repeat the observation if the game changes or your pet setup is different.