when did you know to start timing contractions?

Just curious.  

With ds1 I didn't feel them just went in because of all the pressure.
Ds2 I didn't start timing them till they hurt.
Dd1 they weren't regular when I went in but I thought my water broke.

With my 2nd, I didn't really start timing them until they were fairly regular and they were uncomfortable. I used contractionmaster.com with her but this time around I've got an app I'm hoping to use.

I didn't time them with my 1st, I just went in when I couldn't stand the pain

When my water broke   before that all my contractions were really inconsistant.