Similarly to solving captchas and watching ads. I've been doing it for 5 minutes to see how much I can accumulate and this is what it looks like:
5min ~ 11$
10min ~ 23$
20min ~ 24.5$
So with just a 30min a day you can earn some quite decent pocket money and yes, you can withdraw in bitcoin.
I'd ask you to please use my referral link, thank you.
This website: https://goo.gl/GL34M1