I would advise against splitting the long ride, you won’t really get all the benefits, both physiological and psychological. Although a 4 hour ride on the trainer is also super hard core, longest I’ve done is 2.5 and I won’t go over 2 any more, so kudos!
Any options for flexible working? E.g. Coming in later and working later one day so you can ride before work? Or starting early and finishing early so you can start the ride before 6pm? If you’re traveling a lot with work a lot of employers are prepared to be flexible (since I bet you’re sometimes travelling outside regular work hours?). I’ve done late training sessions and it does mess you up a bit, if you finish at 10pm then you end up going to bed pretty late and/or struggle to sleep well because you’ve just eaten and are still buzzing from the workout.
You don’t mention your long run - is this also being fitted in midweek? Or if you’re doing that at the weekends can you swap to do the long ride at weekends and long run in the week? I did this a lot when I was training for IM, the run is shorter so easier to fit in, and I like running in the evening or early morning when it’s cool and quiet. Also hated having long run and ride both back loaded in the week, was starting to dread weekends, in fact I ended up restructuring my training plan and log to start each week on a Saturday as weirdly that seemed psychologically better!