By precisely boosting off two gates, you can maintain momentum (by continuing boosting) to save up to 3 seconds per flap.

I tried both of them. Second one is definitely faster, but personally I think the first one's actually slower, because.
A: If you take the right path, you can't even hit the rail unless you take a wide line or a slow jump.
B: Going left instead is easier, but that path is slower than going right.
And C: Because unlike the second one, whichever way you take, you are shot into the rail, which slows you down.

You can also do it without boosting, but doing it that way causes you to lose balance.