When do you know it's time to go to hospital?

Last time I was induced so was already there. This time I'll be doing what I can to avoid induction but as I was thinking of it tonight, I wondered when do I go in?

I think I know when I would have left last time. The contractions were never timed, but there suddenly came a point where I said to DH "I think I need to try something (meaning gas)" and then my waters broke. So I think I would have left then, but the problem is I couldn't bare the thought of moving and shortly after I went into shock, so I don't know how we would have gone if we were at home.

If we do manage to start at home, I don't just want to get in the zone like I did, and then leave it to late, but I definitely don't want to go early. If I can get DH to time contractions, when do we leave?