Can you point me to the image of Link walking below water? Only water looking one I know of is just a shot of a Zonai looking Shrine area with a glass like ceiling with water inside or above it on Pg 56. It's just a shot of the ceiling and nothing else.
That's not young Purah. Different character altogether, totally different face, eye shape, and hair & eye color(grey vs white and brown vs red), just wearing the same kind of eyeglasses but missing all other hallmarks of Purah that were present in her BotW Child appearance and now Adult form seen elsewhere in the artbook. Most likely one of the Sheikah kids grown up a few years.
The Sheikah slate is the exact same one modeled after the Switch in all the artwork we've seen, both public and leak. The spool of wire being wearable doesn't really make sense for communication, why would Link need to wear and carry the wire with him to talk with Zelda? Maybe she plays a role, but there's no real evidence of it, just hope.
Plant growth on 119 doesn't require time travel, it's just a mechanic to have plants we could chop down regrow over time as we play. That or simply to have more variety of plant life in the game showing the same plant type in various states of growth. One example on 106 is just a full grown plant rolled up and in bloom. Probably reacts to light/time of day or some other stimuli that causes them to roll up or fully bloom.
Again the building structures are not back to their original form. The Forgotten Temple is fundamentally different, there's a huge gap in the Artbook leak at the bottom that leads to the doorway, that section in BotW is fully bricked up and continuous across the whole structure behind the Goddess Statue. It doesn't make sense that they would rebuild one section to seamlessly and flawlessly match the rest of the structure and then just take a sledgehammer to the ledge above to make room for the Goddess Statue's head. Same for the Great Plateau Northern Wall, it's completely different wall from what was there in BotW, not simply fully repaired or anything. Totally different architecture and structure and no other sections of the wall scene elsewhere in the trailers look to have changed. It's not a cut and dry thing that just time travel can explain to me. Maybe but this is the best evidence we have an it's spotty at best. Not worth seriously considering to me.
Ancient Greek/Aztec/Mayans are most likely Zonai. Might be present day might be a flashback. They have elongated ears compared to Hylians/Sheikah. The Ninja outfit is just a Sheikah guy, normal ears, and doesn't look ancient, it's the exact same out as Link's Sheikah set in BotW.
All the images without a head is still of Link. It's his outfit and his new arm in it. Pg 85 is the Hylian Tunic, 161 is the Rubber Outfit, 166 is the Tunic of the Wild, 193 is the Flamebreaker armor, 202 is Barbarian armor. All from BotW.
Time travel may be in the game in some form, either via memories or direct gameplay mechanic like timeshift stones, but outside of the Forgotten Temple/Great Plateau discrepancies there's really no good evidence of it.
I'm hopeful for the musical items. But they may just be associated to that one circus conductor looking character and not something we can interact with.