If I get momentum before the timer starts and then go off the hoverboard for the momentum before the timer started, would it be a hoverboard speedrun or normal?

It would be considered a hoverboard speedrun. Using the hoverboard glitch has to go under the hoverboard run otherwise it won't be counted. This is because technically you are using a glitch to set the record and the run clearly states glitch less. If you put it in the glitch less runs it would therefore give you an unfair advantage to people who try it without glitches.

If you don't want to read that lol just yeah hoverboard.