To edit the timing of your audio files, you need to turn on Flex view in the Arrange area.
Choose View > Flex View in the Arrange area’s local View menu (or use the Hide/Show Flex View key command).
Click the Flex View button in the Arrange toolbar (if visible).
Turning on Flex view displays the Flex Mode button in the track header of each audio track in the Arrange area.
This button determines which flex mode, if any, is used for processing the audio material on the selected track. For details, see Choosing Flex Modes.