This is even against game mechanism, when you inactive for 15 minutes, the island went to sleep mode, when you log in, "fast-forward" done for last 24 hours, so it is impossible to lose, also, I went on vacation for 10 days, keeping my gem pit running, and started some building upgradings, when I came back the gem pit was not used a lot, got some gems, my buildings were still upgrading, you can try that in test server too.