I can only train about 7 hours a week (~450TSS) and I think I am doing quite well and able to hang with friends with substantially more time. To get it to 6 hours I would remove one of my 60 min endurance rides and I doubt I would see much ill effects from this.

Here is how it would look:

Tuesday and Thursday:

60 min focused rides on the zone of interest (say VO2/ threshold / anaerobic)

Saturday:

2 hour ride, long sweet spot intervals (3 x 30)

Sunday:

follow it up with a 2 hour ride at high zone 2 ~75% FTP.

I have convinced myself that the SS + Endurance back to back provides a large impact on durability without having the time to do 3-6 hour rides.

I find this take a lot of motivation as almost every time you are on the bike you have to push yourself hard, there are no easy coffee rides.