Curious fact: Until this year, it was against the law in California to start across a street after the countdown timer started (or when the red “don’t cross” hand appeared).
That law was mostly unenforced, except in Los Angeles, where the LAPD went after people hard.
A state legislator from down there got a bill passed (and the governor’s signature on that bill) that now allows pedestrians to start across on the countdown as long as they make it to the other side — or can stop in a safe place mid-street, like a median — by the time the counter hits zero.
For intersections with the older signals — those that display the walking man or the red hand only, with no timer, it’s still illegal to begin crossing once the hand starts flashing.