Just a few thoughts on this, not disagreeing, because yes they can do it if they want, but looking at this another way:
Out of what you outlined above I think the TOT to Guardians is the exception, everything but the ride system, was redone at a crazy speed. No offence but Incredicoaster is not a great example as there was not much that was redone as there was not much there to begin with (maybe I missed something or am ignorant to everything that was done). The last two I believe are good parallels to this project 20-30 months for a redo.
So lets look at the likely start date for this project:
Disneyland:
Currently Disneyland is down at least two rides until some point (lets say June) of 2023. When they will also gain the Mickey ride. Personally I do not see them taking more capacity away from the park (especially once you begin to factor in holiday closures for Mansion and IASW) until Toontown is back. So my belief is that the earliest they can start Splash is June of next year. If we go 20 months from then would be Feb 2025 and 30 months would put us at Dec 2025 both outside the 2024 opening quoted. Never having been to Disneyland or California I am not sure how summer heat would factor in their decision as to when to close the ride, push ride closure out till fall of next year and now your opening is in 2026 territory.
Disney World:
Again nothing happing here until TRON is up. So that would put us at Nov of this year at the earliest. Possible for a 2024 opening if that was to happen. However they may hold until after the busy Christmas season so that would put us in Jan/Feb next year making a 2024 date unlikely. From what I remember insiders have already hinted that they are planning on normal winter maintenance on Splash indicating that next year (2023) will be a mostly normal year for the mountain. Disney needs capacity for both general guest sanity and to keep Disney Genie+ as a viable sell. A late 2023 closing would be my guess if it closes at all.
Could I be wrong absolutely, but I think if we look at it from a operational standpoint, there are pieces of the puzzle that have to move before this goes forward at both parks. However if that is the case than a 2024 opening is unlikely on both coasts. Obviously this all depend on the timeline but I would be very surprised if these closures take lass than 20months.