You’ll already be aware that you can cue quickly forwards and backwards if you click the fast-forward or rewind buttons in QuickTime Player. Click each multiple times and you can increase the speed up to 8x, before it will switch back to 2x.
However, hold down Option (Alt) while pressing fast-forward or rewind and you can increase playback speed (or rewind speed) in point increments — 1.1, 1.2, 1.3 and so on. Give it a try.
Fast-forwarding at speeds at up to around 1.3 means the action is slightly faster but you won’t be able to notice very much and speech will still sound OK — ideal if you want to watch a half-hour show but you’ve only got around 20 minutes to do so!