We did something similar to that last year in order for our robot to drive forward for an interval, then stop and actuate it's bridge manipulator.
Anyone on Curie field that saw the big black robot crash full-speed into the bridge during autonomous (twice
) saw how well that worked out.
The best we could tell, any variation that uses up processing speed would make the action take longer than anticipated, and we used a similar method to yours.
I would recommend using encoders