In my experience, work before play is the most productive strategy. Two things that I think might help your situation:

1) Pomodoro technique - I modify this to be 45-60 minutes of work, 10-15 minute breaks. I do six of these throughout the day. When I'm in the work phase, no news/social media/any distractions, focus is important. Do whatever you want in your breaks. And stick to the timers, don't go over on either your work periods or your break periods.

2) If you're doing client work 8am-12pm, stop at 12pm, regardless of whether you've accomplished what you were hoping to. Stopping when you say you'll stop makes it a lot easier to stay mentally focused when you first pick it back up the next day: even if you don't like what you're working on, you know you only have to focus on it until lunchtime, and then you get to work on the fun stuff.