Event Operations : Change Duration : Change Duration Settings : Set/Add/Subtract/Scale Option
 
Set/Add/Subtract/Scale Option
Set All To
Sets all durations to a length specified in quarter notes and ticks.
Add
Adds to the durations by a specified number of quarter notes and ticks.
Subtract
Subtracts from the durations by a specified number of quarter notes and ticks.
Scale by
Shortens or lengthens durations based on a percentage value (1–400%).