The time spacing definitely works on bus routes and tram routes. They don’t use it on cargo or on trains though.
I suppose as trains tend to be rather more “sensitive” to changes than road vehicles, and routes can be potentially rather more complex and specialized, perhaps they decided to disable it. I think it would be rather a good idea to have it as an option you can toggle per-line, for all types of transport. That way you can make use of it to keep a well-designed route working with a balanced timetable, and disable if for any route where an even spacing is going to cause issues.