Definition: Dwell time is the length of time the ball stays in contact with the rubber when the ball is hit.
Longer dwell times are said to be better for producing spin, while shorter dwell times are supposed to be better for producing speed.
The hardness of the blade, thickness and hardness of the sponge and topsheet, and tackiness of the topsheet are all considered to be able to affect the length of the dwell time for a particular bat.