Don’t know if there is any research.
But, to continue the thought experiment, lets say you compare 2 hours every day (7×2h) with two extremely long days (2×7h). My feeling is that you’d quickly build up tolerance for the 2h rides, and plateau. I’m not sure if you can build up the same tolerance for the longer rides (higher dose) and lower frequency of the 2x7h rides.
The other thing is that while a 2h low-intensity ride is likely sustainable with stored energy, a long 7h ride will probably engage more of the fat-burning system and might bring other physiological systems into play to cope with the sudden high load.
(This is something that could actually tested fairly easily with lactate measurements. Get a group of people to eg commute 2h every day for mayne 12 weeks, and a group of people to spend 12 weekends on the bike. )