Hookshot Jumping allows Link to jump while he is standing on a pit. The jump window itself is 1 frame, however the trick can easily be buffered.
Hookshot Jumping is quintessential to learning most Link's Awakening DX categories as its used to skip the Rooster Sidequest, however due to ruleset differences it is not so important in Link's Awakening speedruns.
The buffered method of Hookshot jumping is very easy, however quite slow:
|Buffered HSJ Reference Frames*|
* These reference frames are the best-case scenario. Sometimes the visual cue will fluctuate due to position changes during the Hookshot animation.
If you buffered the Map Menu on the correct frame, Link should jump out of his Hookshot animation. A frame or more early, and nothing will happen - you'll have to mash the Hookshot to retry in this case. Too late, and Link will simply use the Hookshot and you'll be able to try again.
Unbuffered Hookshot Jumping is quite difficult compared to the buffered method, however it saves significant time when done well. This method relies on visual cues, and so can be made quite consistent with enough practice.
|Unbuffered HSJ Visual Cues*|
* These visual cues are the best-case scenario. Sometimes the visual cue will fluctuate due to position changes during the Hookshot animation.