wait until it comes to a boil. the boil time of the wort is not as important as the boil time of the hops. For example, when your wort comes to a boil the hops don't need to go into it immediately, you can wait a few minutes (in case it catches you off guard, lets' say), it doesn't need to be exactly coincidental. Therefore you can boil for like 70 or 77 minutes, or whatever, just make sure that you time the hops correctly, adding them when prescribed.
Bitterness is calculated based on the time the hops are boiled, so the longer they are boiled the more bitterness that is extracted.