How do you measure time to plane, and when do you know exactly when your are on plane...

With a stop watch???? or.......one one thousand, two one thousand, etc........

I like the one mississippi, two mississippi... or the stop watch....

It's measured from you put the power on untill it planes out/rolls over, if that is your question.

I'm assuming the bigger question here is "When are you actually on plane." And yes, there will be some lattitude here. Some boats raise the bow (considerably) then roll over and down. Then you would be on plane. Some boats (I can use the 42' Fountain as a pretty good example) just seem to raise pretty much straight up, so it's kind of hard to call. I would also offer that the props would have to be hooked up for me to consider a boat on plane too.

I guess if my boat was struggling to get on plane, I would be concerned.

Otherwise, I'm usually not in a big hurry to get on plane. I try to keep the RPMs around 3K until I am on plane, the prop is bitting, and get my trim / tabs set. Then I get on it.