[esila]

Taken from "Time Management for System Administrators", however I feel this particular principle applies towards your situation:

Figure out if you're a "morning/mid-day/late-afternoon/night" person when it comes to your brain activity. Some people, for the life of them, can't get their brain functioning when they get up. Others can't seem to concentrate until they've gotten lunch and feel "established" in the day.

Figure out your natural cycle and make sure you attempt to get good quality coding time in during your best times. If this is not possible, then apply the other response suggestions and hopefully you can increase the range of your concentration time.

[allenp]

I want to add that this book has a lot of good advice for all sorts of jobs, if you look at how to apply it. Two advices I like are to list your next day's activities before leaving your work for the day, and to work out a blocking system with coworkers so they handle incoming questions for you so you can spend the time focused. The blocking would be handled in an alternating fashion every-other day. It is a really quick read and written in a conversational tone - check it out.