One of the most productive things I’ve ever done is to set the clock on my computer to analog. Top-right corner of OS X, click on the time, and then click ‘View As Analog’. If you happen to look up, you get a general sense of the time, but not the specific time. This has helped so much. Instead of realizing it’s 2 AM and then thinking it’s bed-time, I look up and get a general idea of the time and continue working.