Using a wait might make everything else stop, I wonder how that would affect stuff like enemy movement...
I'd recommend adding some more logic elements underneath there, I don't have the capx to send you back a screenshot with, but it'd be more like
On PlayerForwardAttack- set lv_currentRunSpeed to PlayerBox.PlatformSpeed
PlayerBox.velocity>=0- set CustomMovement Horizontal speed to gv_speedAttack
PlayerBox.velocity<0- set CustomMovementHorizontal speed to -gv_speedAttack
-Blank-- wait .2 seconds
set customMovement Horizontal speed to 0
Once your'e done with customMovement Horizontal, setting it back to zero should put platformer back into control
Another thing you could do is give the player character a variable that has his current state stored. You'd set it when he turns left, or jumps, or what have you, and check that state when deciding what to set the customMovement to. For that custommovement speed, use either horizontal or vertical, I don't know what overall is supposed to be for.