You can try and get him to work on living in the real world for time by having him either wear a watch or having a clock nearby. Verbally make him aware of the time and that the computer or other activity goes off at x time. Instead of telling him he has 10 minutes, periodically ask him to check the time hopefully instilling that habit when doing certain tasks.
We tried this and it doesn't seem to matter. He can be right next to a clock, alarms will go off, and he will just ignore it all if he's buried in something.
We are working on it, but he just seems to live in a time dilation.
