I assume you’re using an animation state machine from within your AnimBP.
What you can do is when WASD is pressed, leave your Idle state and enter a state that plays your Start animation. The transition out of that Start state tests for the completion of the Start animation (via the TimeRemaining node). When that happens, it’ll transition to your Locomotion state. The transition out of your Locomotion state is the absense of WASD, which takes it back to the Idle state.