For commercial work about a week on average, though i have done some 'crunch' work in as less as 10-12 hours too. Depends a lot on how complex the work is and how much custom stuff i have to build as opposed to using bought/free content.

For personal it takes as long as it takes LOL. Right now i'm using my spare time to work on a project for an online contest that will take me about 45 days to finish. I also have a HDD full of stuff i'v started then lost interest in, so those can be put in the 'never finish' category heh.