I used to believe that too but while 5 blocks of 1 hour each aren't as efficient as 1 block of 5 hours, it's still better than 0 hours.
Today I've managed to get Hadoop set up in pseudo-distributed mode in 1.5 hours on a fresh VM I just installed, while reading a tutorial in the background waiting for stuff to download and install. Tomorrow I'll think more about how I want to convert my crawler prototype from C# over to Ruby on the cluster and read a bit more about how this all works while I wait for code to compile or packages to run at the day job.
Even the 15min I spend eating while at the client are used to think, read and plan my next step or how I will implement something. Same for the drive to/from work. Yup I talk to myself. There's a lot of time in the day when you're supposedly busy that you can get constructive work done.
In the evening I'll start working on getting my first test job to run. At the end of every day it looks like I've made little progress, but at the end of the week I'm certain to be happy with my progress (something I learned from David Burns' "Feeling Good" is to actually test your hypotheses; if you feel you didn't accomplish much, actually test it by listing what you did and you'll be probably be pleasantly surprised).