No, it really isn't. Unless you've a history of quick labours, we don't tell our women to call until they are having contractions at least one every FIVE minutes, lasting long enough that you can't talk through them. And for first babies we mostly say stay at home until you are having 3 contractions in 10 minutes. One contraction every 10 minutes- usually not in established labour, even. It can all stop when it's been like that, and not happen for a couple of days!