About 12.5 hours into playing, the time quests disappeared.

Usually, time quests are only good for the first round. After that, they usually drop to around 1000 gems per 30 minutes. However, in this game, each time quest randomly gives around 5000 gems, sometimes over 10000 gems, so the rewards were quite decent. There's also a hidden quest to level up the main base. Construction is limited to one building at a time, but if you spend 300 gems, you can build an additional one. By running two constructions simultaneously, you save time and can complete it easily. Now the time quests are gone (the last one right before they disappeared seemed to be for 18900 gems), and the hidden quest to level up the main base to level 15 for 20000 gems remains. I guess I'll stop here. Since it's the final stretch, I used up my remaining gems and speed-up items to significantly reduce construction times. Haha It's a shame because I could have played longer if the time quests hadn't disappeared. Anyway, the rewards were good, there were no ads, the game difficulty didn't require much thinking, and it was a playable game for free-to-play players.