Timing disrupts speed. Alexis Arguello is the perfect example. He wasn't fast at all but had great timing.
Timing could refer to several things. I think of it as the triggger and when the boxer pulls it. So think of a moving target and to hit the bullseye you must press the trigger at the right time. So in boxing this could be applied to several instances. One could be like James toney throwing the counter right off the shoulder roll. Or mayweather doing the amazing pull counter, that requires amazing timing and speed. Marquez done a great feignt counter in the mayweather fight, showing how important timing is, he used his timing to overcome mayweather speed of reflexes and hand speed. Another example of timing is when an opponent makes a mistake fundamental mistakes with footwork resulting in imbalance, or squaring up or diving in. Example is cotto dropping clottey with a jab as he squared up, the timing of the short stiff jab is what made clottey fall, not power. Speed is just rate the fists travel, or maybe foot speed or reflexes for head/body movement
Marquez/Pac is a good example, I reckon. (Marquez isn't exactly slow himself, but I think Pac is noticeably faster.)
Ive never been big on the speed idea. If you make the same moves every time , no matter how quick it becomes easy to read. Quick Fighers who were easy to figure out Hatton Judah Khan Fighter who were the best at reading opponents Barrera Morales Hopkins