"Time dilation" is actually a real phenomenon. Most examples involve astronauts travelling at near the speed of light. It's estimated that if a spaceship almost reached the speed of light, 5 years on that spaceship would equal around 36 years on Earth. And actual astronauts have measured that this is real. They've had synchronized clocks on Earth and a space shuttle, and the one of the space shuttle has ended up chronicling less time passing than the one on Earth, because of the difference in speed. Usually the difference is only microseconds, but it IS measurable.
https://www.nature.com/articles/s41526-023-00250-x
https://www.amnh.org/exhibitions/einstein/time/time-machines
https://en.wikipedia.org/wiki/Time_dilation
What you guys are describing isn't technically "time dilation". It's "hypnotic suggestion", basically. You guys are saying that their awareness of time has changed, not the effects of time itself. That it's a psychological effect, not a physical one.
And that...could almost work. It doesn't really explain the Giant's ages, since hypnotic suggestion can only take you so far. From what we've seen, Giants age mentally and physically the same on and off of Elbaph, like with Dorry and Brogy or Oimo and Kashi or Saul. And we still don't have any mechanism that would trigger this. But, it would explain a few things. But, it would also raise other questions.
I feel like time being different on Elbaph because of a hypnotic suggestion wouldn't really explain why the God's Knights are experiencing the same thing, since they arrived on Elbaph in a completely different way from the Strawhats and Giants. Even if it was somehow caused by the pollen of the World Tree or something, I feel like the Gods Knights would know about that, and take measures to prevent it effecting them. Gunko was wearing a mask, so that kind of thing likely wouldn't effect her. Sommers is wearing shades, so it couldn't be the light. Qilingham was wearing a helmet, so it likely wasn't the air on Elbaph. None of them ate anything except dream food. I'm just not sure what the "trigger" for this kind of thing could be.
(This is a tangent. But, when you think about it, the God's Knights are kind of like the Three Wise Monkeys. "Speak no evil", "See no evil", "Hear no evil".)
https://en.wikipedia.org/wiki/Three_wise_monkeys
Plus, if there WAS some sort of "physical" time dilation or "psychological" hypnotic suggestion in place...shouldn't Imu be moving MUCH faster than everyone else, right now? Imu is not physically on Elbaph. Imu is just mind controlling Gunko's body. So, Imu should not be affected by the "time dilation", in whatever form it takes. Imu should be able to puppet Gunko's body at hyper-speed. Causing her to zip around and be almost unintelligible when she speaks, since she's moving 3 times faster than everyone around them. But, Imu isn't moving that fast. Imu is moving at the same speed everyone else is going at. So, either Imu is CHOOSING to move MUCH slower than they naturally would. Or Elbpah's time dilation is effecting Imu, even though they're not even on the island, somehow. Or there is no "time dilation" effect at all, and Imu is puppeting Gunko's body at a normal speed because time is moving at a natural rate. Phsycially AND psychologically.
This IS a story. So, it doesn't have to strictly adhere to actual real world rules. Still, it would be best if it was at least internally consistent. And I'm just not sure this would be, if Oda chose to go in this direction.
And either way, this still wouldn't help the Strawhats train. The Strawhats would be better off training LITERALLY anywhere else, if they wanted to get stronger faster.
All that being said, I would LIKE to find a way to explain the possibility. If only to say that I COULD if I wanted to. As a creative writing challenge. So, as a thought experiment, lets see if I can explain how Oda could make this work.
Thinking about it, there IS actually something already introduced into the story that could explain a actual "time dilation"-like effect on Elbaph.
Foxy's Noro Photons.
https://onepiece.fandom.com/wiki/Noro_Noro_no_Mi
Yeah, Foxy might actually become important in the story. I'm disgusted, too.
But, the Noro Photons can slow people down. It's a slightly different effect than what's being proposed for Elbaph, since the people Foxy hits with them are still aware that they're slowing down. But, it is similar. Similar enough for Oda to use it, at least with a twist.
And Yggdrasil is another tree similar to the Sunlight Tree Eve. Sunlight emits photons. There is...a logic to this, if Oda went this direction. We haven't seen the tree emit any bright lights. But, Elbaph DOES have the Sunstone Painters that can make physical rainbows. And rainbows are just refracted light. Maybe one of the side effects of making physical rainbows with the Painters is that it screws up time around them, producing Noro Photons? This kind of thing might still effect Imu, because space-time itself is affected by the presence of the Noro Photons. Since they're photons, just "looking" at Elbaph might be enough to effect a person.
Noro Photons, being a fictional particle, could slow people down without them being aware of it, but still allow them to age at a normal rate. They'd be moving in slow motion, but their bodies would still age at the normal speed. Fictional particles can do a lot of things, if you decide they can!
So, could using the Sunstone Painters actually cause time to warp around Elbaph? I don't know, but at least doing it that way would actually explain how it could work. It explains it more to my liking!
I'm still doubtful about it, though. There's just too much about this idea that just doesn't add up. It just feels contrived and contradictory. And it doesn't really help anyone. At most, we get a kinda-sorta timeskip out of it, and we see the effects of the Strawhats going missing for a week. I could be proven wrong, though.