When thinking about the stroke should there be any stops or starts? Does the handle and seat ever stop moving? If so where is it ok?
Ideally the rowing stroke is a cyclical motion that is fluid and dynamic without beginning or end. When thinking of the catch you should be thinking of the weight coming on to the feet and being ready to push as soon as the shins are vertical. Try to imagine your seat changing direction without any pause. The only time the seat should pause is when you have pushed the legs down and are finishing the stroke. Thinking of it like this the beginning of the stroke might be considered bodies over as the seat begins to slide or half-slide as you approach the catch on the recovery.
If you have time today, take 5 minutes to row in super slow motion feeling and thinking about the timing of the seat and hands. Your goal in developing an efficient stroke should be smooth, continuous motion without pause or hesitation.