@IreneSwift Hello again!
In one of your first posts you mentioned that you did not finish the first opportunity given by Emit/Time, and I disregarded it, partly because I did not remember the adventure, having done most of them, and partly 'cause I thought that The Sims is not a linear game (most of the guides I've found on ITF recommend doing the first opportunity-adventure line, but don't mention why) but that was a bit sloppy, so I tried again. This is what I did:
In a new save, in Lucky Palms during summer, with a saved sim from library that could fish, I called upon the Time Traveler, did what he asked until he wanted me to excavate the debris piles, did not do that. (They are one-slot grey-brown metal trash piles spread out in the waste lands, not visible from map view and two of them can be found behind the hill that contains the mysterious door). My sim was by then 'best friends' with Emit and had less than 1 skill level in advanced technic (in the first test run my sim had level 9).
Instead I went home to current time, bought the Life Time Reward 'Time Control', changed the future to dystopian, went there, directly saw the debris piles on the water, in several places, they showed '3-eyedfish' when examined, caught one (same place as before, outside the gallery).
Went home, changed to utopian future. Flowers were not there at 20:00/8 pm. Waited and they appeared in front of my eyes at 00:00/12 am. Examination showed 'rainbow snail', fishing was successful.
Went home, changed to dystopian, no debris piles on water. My sim waited by the water in front of the gallery from 07:40-09:30 in the morning, live-mode, then they appeared and fishing was successful.
Bought a lot (while in dystopian future, the one next to The Dunes residence, by the Waste Lands), went home, changed to utopian, no flowers on the water anywhere. My sim waited by the water in front of the gallery from 11:40 to 13:40 for in-game real-time, then they appeared in front of my eyes. Examined them and fished rainbowsnail. Nowhere else I saw any flowers. In the lake where I had seen them the previous test run the same spot showed only ordinary fish when examined.
In game-real-time I zoomed in and out from map view looking for them and they slowly started to pop up (almost as a response). At 17:30 there were a lot of them and also visible from map view (small flickering light spots), they showed 'rainbow snail' when examined, and my sim could fish successfully from the lake.