^^Chavez didn't wait. The problem was Martinez lateral movement and his speed. Also, chavez landed probably harder shots than he did in the 12th several times earlier in the fight that didn't phase martinez at all. The difference was Martinez look exhausted by the start of the 12th. He just threw 108 punches in round 11, plus all that movement took a lot of energy. So that knockdown chavez scored probably had a lot more to do with Martinez being very fatigued.
Which means if chavez "started earlier", he would have got beat up even more and possibly knocked out himself.
In short, there isn't any possible way chavez could have beat martinez last night, other than what he nearly pulled off in the 12th. That was his chance and props to him for coming close. But Martinez got up and popped chavez something fierce with a left that stopped chavez in his tracks. A lot of people overlooked that. Martinez after getting dropped, kept fighting back and rocked Chavez pretty good, which slowed Julio's output from that point till the sound of the bell.