The consensus is that you'll need to delay that until WoTLK Gold after you've burst your window since if you lose the icy veins due to their keenness and also a potion of speed, you're bound to go over the limit.

Therefore, you should delay the buzzer's for a while and then, once you get embrace of the spider change the speed potion into a potion of Wild Magic, and that should be enough to break up the cooldown of your haste, so you're not wasting a lot of haste.

Also, for these burst windows, even if you're losing around 30 haste per hour, that's not much of a thing. It's probably worth using the haste available in the burst window to maximize your burst window buy WoTLK Classic Gold. But at some point, you're using time and effort, which is going to be an DPS loss, instead of segregating them.