Maybe KidLogger is suitable for your situation, if you have access to his PC:
KidLogger. Free keystroke logger, web
activity monitor and screen capturer.
Very simple, free and open source
key-logger (keystroke logger) program.
Designed for home family users and to
keep watch on kids (2-7 years)
activity on the computer. It can log
all websites visited, chat rooms
talks, started programs, opened
documents and windows viewed pictures
and movies. It is also a simple and
FREE key logger and activity
monitoring program for family needs.
I don't know about time spent, but most loggers will show you a time beside each event, so you can just see when he visits a new site and compare times.