Weird Hidden

I didn't get any hidden quests for 4 days on the Time Quest, but suddenly today, when my level reached 7, a hidden quest appeared. Things that wouldn't have happened before are happening lol. This makes you think 'what if?' and start expecting things. I have some 500-gem Time Quests without hidden quests, should I do them? lol I really don't know the reason. I just hope hidden quests appear based on an absolute standard.