I used to only be able to program in large blocks of time also.
Then one day I thought about the 66 minutes I 'waste' each day on the train to university; 33 minutes per trip. I started to take out my laptop as soon as I get on the train and try to work on programming. Initially I had very little done, by the time I really start programming it was time to get off.
But now, 3 or 4 months into it, I seem to manage to get something done every time; I'd say now the 33 minutes is worth at least 20 minutes of productivity if I had been spending it in a 4 hour block.
Parkinson's Law - work expands (or contracts) to fill the time available for its completion.
When I was teaching English, for one class, I gave groups a human-slide puzzle activity. A group of 8 were given a number from 1-8 and arranged randomly on 9 numbered squares. They were to re-arrange themselves in order by moving one person at a time to the empty square.
The last group to complete it was having a really tough time and kept complaining to me that they couldn't do it. After all the other groups had finished I announced they had 5 minutes left. They completed it just before the time was up.
I have the same experience! You start to anticipate arrival and focus on "cleanup" work at some point. It happens so naturally that you hardly notice. If there is something left to be done, it's usually something small, like a 5 minute task.(maybe the train was early?)
Then one day I thought about the 66 minutes I 'waste' each day on the train to university; 33 minutes per trip. I started to take out my laptop as soon as I get on the train and try to work on programming. Initially I had very little done, by the time I really start programming it was time to get off.
But now, 3 or 4 months into it, I seem to manage to get something done every time; I'd say now the 33 minutes is worth at least 20 minutes of productivity if I had been spending it in a 4 hour block.