How to check when Candy Crush level get cleared

If you ask your Facebook friends, they'll be prompted to play the game. If they refuse or have blocked the app, you won't get the ticket. If they play, (I believe) they can give you one ticket towards each ticket checkpoint without any impact to their game.

In addition to spamming your friends and spending real money, you can also earn free tickets by replaying levels from the previous set in so-called "Mystery Quests".

Update December 2014: You must be completely offline (ie, no 3G/4G/WiFi) in order to see Mystery Quests, now that King has added the "Kingdoms" feature to Candy Crush Saga. It is no longer enough to log out of Facebook!

After passing a quest, you must wait 24 hours before you can try the next. I've heard multiple people mention that you can skip the wait by modifying your device's clock. There's a particularly complete description of how to do this in a comment here.

Once you've cleared the three bonus levels, you'll be allowed to continue.

You can try as many times as you like, but once you complete the level, you need to wait.

I literally just posted an answer on how to get full lives instantly. The same concept would apply here...If you wanted to play multiple quests per day, you can change the date to tomorrow in your Date & Time settings and you will be able to do multiple mystery quests. Just make sure to change the date back. Hope this helps!