I have a cousin like this. She is ALWAYS late. So when we have something to do, we always tell her to be there half an hour earlier than we tell everyone else. This works like a charm. She still hasn't caught on. Don't hate him too much. There are worse things he could be doing.

Yes, that's an excellent idea. When I try to get up in the morning I wait 20 minutes until I'm finally ready to get up. So, I forwarded my clock 10 minutes and it has helped with the staying on track routine. I thought I was the inventor of this technique but I see I'm wrong. Being late is always an issue with me.

When I had a friend who was always late, I started to look into it to see if I could help him. This drove me crazy and really bothered me a lot since I didn't like being associated with the 'late guy'.

I found out that what I would call a 'pattern' is really more like an 'addiction'.
Some professionals even say there is a 'passive / aggressive' disorder mixed in there too.

I guess there are so many ways of labeling this, because there are so many reasons for people to do this.
Try to find out why he thinks the way he does about being on time.

This site has a list near the bottom of reasons people give for being late. I would print out this page and go over it with him.
http://www.thefreelibrary.com (I couldn't link the page I wanted, but just type in 'chronic lateness' at the page header and it's the first article... sorry)

And... the next event that you both are invited to, I'd just leave at the proper time and hope that he follows!
It also offers an exercise (at the bottom) to help change the tardiness mind set!

I personally think the clock changing trick just perpetuates the passive aggressive behavior and leaves you to do the 'voodoo math' in your head!

It is possible to help him with this and save your sanity at the same time.
Good luck!

(found two more links with ideas on changing the 'late mind set')