Dwell time or hold time is the amount of time between a catch and a throw; the amount of time a prop spends in the hand. This can be anywhere between 0 and 2 beats.
Dwell time is usually expressed as a fraction, called the dwell ratio: the ratio of the time between a catch and a throw made by the same hand (how long the hand is holding a prop), and the total time between two throws made by that hand. The dwell ratio can be anything between 0 and 1. People usually juggle with a dwell ratio of around 2/3.
The speed of a pattern can be changed without changing the height by changing the dwell time. A longer dwell time makes the pattern slower, and a shorter dwell time makes the pattern faster. It's easier to juggle with a fairly high dwell time for several reasons:
- It reduces the speed of a pattern at a given height.
- It reduces the number of objects in the air at a time.
- It allows more time to prepare the throws.
- It reduces the time that each object is not directly controlled.
- The downward motion of catching quickly reverses the upward motion of throwing, making the pattern smoother.
The main disadvantages of juggling with a high dwell time are that the rhythm doesn't work as well for siteswaps with 1s (the maximum possible dwell time after catching a 1 is less than it is for other throws), and there is less time between throwing and catching with the same hand, so it can be harder to get your hand back to the right place to catch in time if you're not throwing close to where you're catching.