This is a shortcut property for defining the pauseBefore and pauseAfter values in a single assignment. The two values should be space separated. If you only specify one, it will be assigned to both properties. If you specify two values, the first is used as pauseBefore and the second as pauseAfter.
The values are specified as time units. These are a floating point value with either the ms or s suffix to denote the unit of measure.
You can specify a percentage value which is used to calculate a proportion of the time taken to speak a single word at the words-per-minute rate defined in the speechRate property.