Instead of Value Type being a Digital (bool), set it to Axis1D(float) (1st pic). So your 2nd pic would then send 1 for Up and a negated 1 for Down.
The next time the player presses the key, the actor will move another 50 units.
Not sure if that’s the part of the ask, but that’d be:
IA's Started -> isTimelinePlaying -> False -> Play Timeline from Start
There’s probably 10 different ways of doing it, though - Lerp, Tick interpolate, Timers. If it’s supposed to be a precise 50uus increments, I’d avoid navmesh. A timeline would be the most consistent, easy to use and still quite flexible.