I think there are workouts that require you to design a route around the intervals (or even just up and down a single hill) and there are others that are more flexible and you can massage to fit into a route.
VO2’s are probably something that you should design a route around. The rest intervals are pretty important as you don’t just want to scatter 5 3 min intervals throughout a 2 hour ride.
SS workouts however are pretty good to fit into the “ride up a mountain then ride to the next one” type rides. You can split up the intervals and do 20min up one climb and then after an hour of endurance you can do another 20min up a second climb. The rest intervals don’t matter a huge amount with this type of workout and in the end the goal is just to get better at sub threshold efforts. And if you want/need longer intervals then just start going hard 5 min before the climb.