Let's say I schedule a meeting from 2-3pm.  Let's say you're running late.  Unless your presence was specifically requested or you have a significant contribution to make, I'd say the latest you should show up is when the meeting is 75% over, which in this case is 2:45pm.  After that, it's completely pointless for you to be there, and in most cases your presence will be an unwelcome disruption at an inconvenient time (attention spans seem to hover around 30-40 minutes).  And under no circumstance should you be like a colleague of mine and show up exactly when the meeting ends.  Some people's actions defy all logic. #business