i doubt malmo will give you much advice on this as I don't think he has cross-trained much in his life. AFAIK, he has dealt with a lot of injuries over a 20 year career, but didn't get into biking or swimming much.
The only thing that will affect this is the "stepwise nature of endurance training". Wejo's coach wrote a great piece on it on this site. I read it year's ago and it echoed what I had long felt from personal experience.
In essence it said:
Running for 30-35 minutes is only marginally longer (or say 30% more time) than running for 25 min. but the development and cumulative effect is so much better that it is far and away worth it (in terms of time spent and wear and tear).
... and running for 50 min is better, and 60 is even better, but in terms of physiological bang-for-your-buck the 65-70 minute run is so much better that it is what you should strive for.
Hence, once most runners start getting really good they won't run for shorter than 4-5 miles and as malmo has stated: he likes to run for at least 10 miles once per day. Tony Benson's book has a good discussion about the cost/benefit of different durations and he says that the cost of a run longer than 15km/10miles is not worth the benefit. In other words it is too hard on you to do but once a week. Now many Lydiard disciples and heavy trainers like the 1.5hr/15mile run ... but that is too much to get into here.
I think it matters what training you are doing. If I was biking I would do the 2 hours all at once. If I was rowing I would probably divide it into 10k (40 min) in the AM and 20k in the PM. If I was swimming I would probably also do 40 in the AM and 1:20 in the PM.
You need to find the sweet spot for whatever activity you are doing. Physiologically I don't think there is a correct answer that is "right" all of the time.
It is just like all the threads about "what is the best way to run 100 mpw?" 5 and 10? 8 and 6? 6 and 8?
I have found that it is best for me to keep volume fairly constant, or say at 12-20 a day and that I don't need many days at just 5-6 (I can recover on 10-15 easy) and I can't handle many days at 20 to 25 before I get wiped out.
It is the same for me in cross-training. About 40-60 in the AM and 60-70 in the PM seems best for me. 2-3 times per week I have one workout that is 2-5 hours.