Unfortunately, there isn't always a lot of warning before labour, and the pre-labour signs that do come, can take a couple hours or a couple of weeks. You can read up on the usual pre-labour signs in the articles section here on BB. They'll give you a bit of a clue if anything is happening. But the time frame is really indefinite. That's the tricky part.
I'd definitely line up a back-up coach - maybe get a doula? Would there be any way for you to keep closer contact with your DH during the last weeks of your pregnancy, just for peace of mind for both of you? I'm sure he doesn't want to miss his baby's birth either!
All the best for a lovely birth, WITH your DH at your side.