Its very simple if you are a webmaster just think about a guy working in a office for 8-10 hours same like him its your job to sit in front of your PC.
I spend a good 8+ hours infront of a computer at work. And an average of 2-4 hours at home, depending on the day.
About 5-7 hours a day ( in summer ) but when is school, about 3 hours a day... Working on sites, chatting, playing games, chatting on forums, learning PHP, watching news...
isn't good, but what we can? expecially people who works with PC - 8 hours on work + when they got home, games, forums, chat, news + website ( optional )...
I would say that i spend about 12 hours a day while building up our 35 websites but this will decrease over time as things really start to pick up then i think about Christmas time i will be able to drop it back to 3-4 hours a day while doing the normal routine jobs on the sites.
the worse is when the site is new or when you do refreshments ( new desing etc. ) but when you stabilize it and especially if you have CMS, you spend only about and hour a day to add new content...