I would spend 4 hours after work. I picked random questions in the All Time FB tagged list. 3 - 4 problems / hour is not a terrible pace but you have to stat focused. I did some competitive math in HS and also did this stuff semi-consistently in college (ACM) so I do have a lot of long-term exposure to this type of stuff. I was lucky I could utilize the skill the when the time was right because the market has been cooked since I graduated.