Time starts when you gain control of your character. For PS versions Alucard delay would vary between 8 and 11 seconds, XBLA 3-4 seconds. Lower for Richter.

In-game time starts slightly earlier than that, so keep in mind that if you don't do any actions that pause the IGT the clock will start opening at around 7 minutes and 58.3 seconds.

Time does not start at first input, so you can not wait in the prologue to assure clock room is open.

Time ends at the killing blow for the last boss (Dracula or Shaft) with the exception of the ACE/Save Corruption run, which ends at triggering the final cutscene.

This differs from TAS timing, which begins at system power on.