Name of Space travel mystery abt missing planet?

[dancingcranepa]

I'm trying to find the name of a scifi book I once read. The protagonist was a pilot with a copilot from a different planet. They were accompanied by two of the golden bjor race. A planet is missing and it turns out it was hidden in time and the protagonist is the son of the leader of that planet. The 2 lead characters fly channels between the planets that grow over time but something is breaking them up. A tree connects the points in time. The phrase "web between the world's" sticks in my head but that might not be this story. Can anyone help me find the name of this book and author. I really enjoyed it.

Thank