In general SPEED = LENGHT / TIME.
In your case Speed = SplineLength / Duration. Or better **Duration = SplineLength / Speed **
Then you should make a variable **float Speed **for your Actor class, that you can edit from Editor.
Inside the graph, you have to set **Duration **variable as SplineLenght /Speed at Event BeginPlay
In that way you set Speed for you actor and the duration is adaptive based on the desired Speed.
S.
