Right now, the rules state that the timing starts when you ready up in the lobby menu of Connected mode. I think might make more sense to start the timer when the gameplay actually begins, when the boss / player boards appear, because:

1. there is load time between the lobby and game screens which can differ
2. there's around 20 seconds there that isn't at all gameplay
3. this means you have to exit back to the lobby every game to get the proper timing, instead of just pressing "continue"