Zelda's lightning kick has a strange animation that sharply raises her ECB then drops it slightly immediately following. Timing this change in ECB near a platform can interrupt the startup of a kick, land zelda, autocancel for 4 frames, and leave Zelda actionable on platform. This is likely the fastest way to land and be actionable on a side platform on all stages.
Fair AI is extremely useful if not critical in the modern meta to bring Zelda up to speed. It is her fastest way to reach a side platform on any stage and drastically improves her mobility and power, as being on platform is one of the best places to be to maximize Zelda's power and mobility. In addition, fair AI enables speed enough to uthrow an opponent to a side platform, fair AI, and techchase grab. It is also exceptionally easy to buffer shield drop from, and you can quickly warp to platform and begin passing through it to maximize your movement and attack options.
The most influential stage to apply fair AI is battlefield. The fastest possible AIs are 2 non-overlapping frame perfect windows, either doublejump on frame 5 after jumpsquat and fair on frame 4 after double jump, or frame 4 and 5, respectively. Actionable on the platform on frame 28, counting the first jumpsquat frame as 1, every other option to be actionable on a side platform is slower, with a reasonably lenient window to input a slower AI and be actionable between frame 33 and frame 39, making it reasonably safe to attempt without the risk of floating upwards inactionable through platform throwing a kick.
The speeds of options to be actionable on battlefield side platform:
Fair AC AI: Frame 28
No-Impact Landing: Frame 32
Uair AC AI: Frame 33
Similar frame advantages are available on other stages. Other stages also afford the ability to waveland off of side platform and fair AI onto top platform; battlefield's top platform is too high to do so.
Fair AI is also one of the strongest albeit hardest ledge options Zelda has available to her, granting 7 galint (frames of invulnerable actionability from ledge) on a stage with flat walls, 9 galint on yoshi's, or 13 galint on battlefield.