If it takes 4 seconds to get to act 4, then I estimate it would only add 2 to 3 seconds to instead take RoF and pop 2 chests.
You are going to Act 4 regardless of whether you are going to town or the RoF WP. The extra time it takes to go from the WP to popping the chests is what you need to know. I'd guess it's anywhere from 5-7 seconds for the average player.
RoF maps don't vary as much as lk. You either have 2 chests below the waypoint or you don't. The goal is to roll a map with that, and 2 huts in LK. The huts don't have to be perfect, just feasible to get cast a tp or use waypoint IF your lucky.
The problem here is with sacrificing LK efficiency to get an RoF map. Losing a few seconds in LK over thousands of runs would, in my opinion, negate any efficiency you may gain from adding RoF. Of course if you get very lucky and score some Jah/Chams that goes out the window, but in terms of likeliness I don't think that's high.
Another problem with this is that RoF monster densities can be a real pain. If you get a map where the bosspack densities tend to be a bit high in the superchest area, you're either skipping a chest or aborting fully on a semi-regular basis. Again, it's doable to get a fairly efficient map for both areas, but you have to compare it to having an ideal LK map since that is the alternative.
Once I get my characters leveled, I'll do some runs and see how hard it is to roll a map. From the stress testing I did, I found 6 Jah and 2 Cham after about 80k runs. This means you can score one every 10k runs or so. The big appeal is cubing a Cham or Zod without having to waste ber runes.
Not having to waste Ber runes is a huge benefit, and that would be the kicker here for making this a good alternative for those looking to cube a Cham/Zod. Maybe for those niche runners that are looking to cube that high this could challenge cows/Trav but I'm skeptical of that as well. Well, let's see.
Let's assume you get lucky and get a Cham after 10k runs. For posterity's sake let's assume you have a damn good map/char, are focusing on runes almost exclusively and can do these runs in 30s (25s LK/5s RoF)
10k LK runs gets you 10 Surs and 2 Bers according to the averages. That's 3 Jah's, or 1 Cham 1 Jah
The RoF portion would get you (let's assume the high end) 1 Cham, 1 Ber, 3 Surs (this is mostly a guess, I could be way off)
Total with all cubed: 1 Zod 1 Cham in 83.33 hours.
We can look at it another way too, how many runs would you need to get a Cham in at RoF to compete with just LK? Meaning, how quickly can you cube a Cham from LK alone? well you'd need 4 Ber's total.
6k runs gets you 6 Sur 1 Ber which gets you there, and has a bit of room for bad luck Ber-wise.
6k runs at 25s = 41.6 hours
Do that twice and you have a Zod at 83.2 hours. This is higher than Gripps calculation above because I'm assuming that you either get a Ber or you don't after the ~3600 runs, instead of counting "half-Bers". Not sure which method would be more reliable, math and I don't mix very well.
Here's the kicker though, if you focus on LK you can get an even better map and run at 20s. This would net you a Zod in 60-65 hours. Add in another 20 hours or so and you'd have yourself another Jah rune.
So that would leave the comparison at 80 hours ran, generally:
LK only: 1 Zod 1 Jah
LK/RoF: 1 Zod 1 Cham
So did I just prove myself wrong? It depends. Basically what happened here is that it's no faster to find a Zod through RoF running unless you get lucky and drop a Cham/Jah before the 10k mark, since you'd get a Zod from LK by then anyways. Keep in mind this is considering you get a damn good LK/RoF map combo, which who knows how much work that will take. It's also assuming you pop a Cham after 10k, which is on the lucky side IMO.
So it goes back to the age-old question. Is it worth it for you personally to try for the lucky drop, or to take the more consistent method of LK? My take is that if you're running *ONLY* for runes and that's all you're picking up, add in RoF and hope for the best. If you're charm/jewel hunting too, straight LK is probably the best method.
All that said, I really enjoy RoF running and hope people actually put this to the test (I might do some myself too). It would be really cool to have concrete numbers here and see how much we could improve it.