Thanks! I'm glad you like my explanations. Since I've written them, I've gotten to play The Smoke Room, Build 17, and Arches, Build 3, so they have developed further and changed slightly.
Spoilers!
Long Post incoming so be prepared :)
I half agree with Flynn not going through time, but this is due to what is revealed in Jenna's route. Flynn/the spirit of Sam possessing Flynn become the Red Socket Faced creature (RSF from here out) at the end of Flynn's route and they jump around to witness and interact with multiple events. Based on what we see in the game, the RSF shows up in Leo's, Flynn's and Jenna's routes, with us seeing its perspective in Flynn's route. This leads me to believe that the RSF tapped into whatever powers the Hysteria/Hum of Echo and jumps not only through time but alternate universes. The RSF was created only at the end of Flynn's route but knocks the group into the lake for both Leo and Flynn's routes (Before it was created) and was seen throughout people's childhood (TJ mentions it in Flynn's route and Jenna's route mentions multiple people saw RSF during childhood). It is also heavily hinted that the RSF in the other routes is the same as the one created in Flynn's route, as in Jenna's route the RSF is heavily protective of Jenna and for some reason Flynn never sees it in Jenna's route, with it disappearing whenever Flynn is actively with the group. I think that the reason why the RSF was created at the end of Flynn's route is due to three things. One, Flynn's need to know what happened to Sydney at the cost of everything good in his life (ex: Carl and Dax), Two, the spirit/simulation of Sam's belief that Echo needs secrets and him trying to push Flynn into creating more turmoil (Ex: The Condemn Chase scene), and Three, whatever powers the Hysteria/Hum appears to feed off of negative emotions/thoughts and uses the RSF as a source to feed from. The RSF is not fully in control of where it gets taken, as we see from it's perspective in Flynn's route, and was initially taken to multiple events filled with misery and negativity. Eventually the Flynn part of the RSF was worn down and barely giving input anymore when they were finally taken to the day Sydney drowned. Once there the RSF's eyesight was stolen from it just in time to deny Flynn to see what he desired to know most, leaving him miserable and filled with negative emotions (which the Hysteria/Hum would love).
As for my Route 65 timeline theory, funnily enough the Smoke Room and Arches also now kinda fit into it as well. Looking at the Echo Universe Timeline we assume that it branches with the choice that Chase makes at the river in 2015 of which friend he follows, however, both Flynn and Jenna's routes reveal that Chase's past is different as they are continuations of what occurred in Route 65. Route 65 appears to be the initial timeline split for Chase, when he decides who he comes out to first. What we see in Echo for Saturday through Monday when the group goes to the river, isn't the same timeline, but instead 4/5 parallel timelines that overlapped for that brief period and then split back off from each other. We see in every route that Chase is slightly different and that is likely due to him being closer to certain people after coming out to them first. For Carl's route, Chase uses more swear words and is a bit more playful with Carl, TJ's route Chase is the only one to get possessed by the 'Mirror Ghost' and is also the only one to admit to killing Sydney while all other Chases appear to not remember, Flynn's route Chase is more aggressive and pursues multiple opportunities to be with Flynn as well as call Flynn out on things while other Chases tend to be more reserved with Flynn, and Jenna's route Chase mentions having spent time with Jenna after he came out to her by reading manga with her and having deep conversations, however, in all other routes Chase is noted to have basically ignored all his friends after dating Leo. The other friends in the group appear to be slightly different based on the route, for example: Flynn is obsessed with Sydney to the point to sacrificing his life in his own route, while he lets it go in Jenna's route or TJ in his own route never mentions the RSF and instead leads the group's scavenger hunt to reveal Chase is Sydney's killer, however, in Flynn's route TJ is more focused on the RSF and barely even mentions seeing 'two brown bodies' in the water. All of this makes me question if the timeline split for the group starts with Route 65 or if instead it happened before they were even born, and each route is just a parallel version of the group.
I bring this up as The Smoke Room varies a great deal based on who's route you are on. While the game isn't finished it is unlikely each route is going to converge towards one ending, meaning that there is another timeline split in 1915. Arches also fits into this as Cameron and Devon are shown in the Epilogues of Leo, TJ and Flynn's routes. However, in all routes there are details showing that they cannot be the Cameron and Devon we see in Arches. Leo's Cameron and Devon are in Echo in 2017, while Arches takes place in 2020, TJ's Cameron and Devon mention the Hysteria taking place in 2017, while Arches states it happened in 2015, and Flynn's Cameron and Devon are in college working on a project, when Arches has Cameron and Devon at age 25 and firmly being out of college for at least 3 years. This shows that those routes not only are following a different timeline than Arches but that Cameron and Devon's age is also different dependent on the route/branch of the timeline we are following.
TLDR: I think that Echo's universe is following a massively branching timeline where multiple branches run parallel to one another for a good chunk of time before they diverge off from each other again. Thanks for reading my Thesis on Echo's timeline! :)