The time it takes completely depends on how fast your computer's processor is, how much and how fast your internet connection's upload speed is.
The more RAM and hard drive space your computer has, the more photos it can synth together.
Also note that if you are running Windows xp SP2, there is a bug with Windows Imaging Component. Either install Windows Live Photo Gallery or upgrade to Windows xp SP3 if you are getting errors about running out of memory with very few photos.
The more specifics you can provide, the easier it will be to help you.
What operating system are you using?
How fast is your processor + how much RAM does it have?
How much free hard drive space?
Are you getting any error messages? (If so, what are they, exactly?)
You say no progress was made? What do your log files say? Type %temp%/photosynther in your Windows Explorer address bar and press enter to view your logs.
Big synths can take quite a while but there may be some other problem.