Timing them is a good idea. (I am sure you already know). I would call the dr - just so they know whats going on.
with my DD I started with BH around week 34 - they werent the real thing for sure
(did I read somewhere before that you didnt have BH with your lil girl?... I could be wrong and it was maybe someone else?)
anyways: my dr says contractions every 5 minutes. He also wants me to time the individual contractions to note the peak.