There's a thread about this in the playback forum. Basically, you have to first enable it in the menus (settings/sound settings/timestretching), then reboot your player. Then, while playing a song, switch to the pitch screen (on my h120 the key combo is play+up or play+down). In the pitch screen, you have to hit the button to cycle through modes (on h120 it's the A-B button), from percent to semitone to timestretching. From there you can change the timestretching settings.