Considering I've been struggling to concentrate recently, this is absolutely the most difficult part of the process for me right now.
My best tool for clocking productive hours when it feels impossible to do so is to wake up early and do it first thing. There was a while where my default wake up time was 5am. Which, considering that I'm self employed and working from home, seems insane but it works. If I open my eyes at 5, I can definitely be at my desk with a cup of coffee by 6. That leaves me with about 2-3 hours of uninterrupted work before the rest of the house gets rolling.
Getting just a few hours of concentrated, high quality work time in the day can mean more than 8 hours of locking myself in the office with all my distractions tugging at my brain.
I really like having this special alone time in the morning, so for a while I thought that this would be my schedule all the time. The problem is that if I have a tiring day, I'll often pass out on the couch before my kids go to bed. It's annoying for everyone, so rather than push myself to sacrifice sleep, I just try to keep regular hours unless I'm on deadline.