This still isn't it but it supports not doing two combo workouts in a week because, extrapolating from what Tom wrote, that would set up a peak at an unknown time but in less than 4 weeks. I also think the answer is different for a miler (someone with a pretty good 400 PR) trying to race 5k and a marathoner (who will never break 60 for 400m) trying to race 5k. It might be good for a miler to run two combo workouts every other week but only one on the off weeks whereas anything more than one a week would doom a marathoner. Of course, this is where it is better to hire Tom because he would know if it would be better for a miler to put in a second combo workout every 2nd or every 3rd week. Tom wrote it for a sub 34 min 10k runner trying to bounce back quickly from injury.
"10k runner -
Hmm, interesting question!
Your base is sub-par but you have an important 10k race in 4 weeks. So, that means you have to work on aerobic capacity (endurance) and elevate race-pace strength and efficiency in a short time frame.
I suggest this:
Throw away 7-day training weeks and go to a 5-day rotation. Every 5th day is a key workout. Since you are limited on time, do COMBO workouts, only. That is, combine various training elements into one workout. I've used this in my coaching since 1989 and found it to be quite effective!
Runn 2-3 miles to warm up, then do some striders. Next, do the core part of your workout. Here is a sample:
2 x 1600m at CV pace, jog 400 between, then
2 x 1200 at 10k pace, jog 400m between, then
2 x 800m at 3k pace, jog 400m between, then
2 x 400m at 1-mile pace, jog 400m between.
2 mile jog cool down.
Typically I do not recommend a long run when doing the 5-day rotation. If you want more volume, I suggest you add a run in the morning before doing the workout I suggest. So, for example, if you did 5 miles EZ in the morning before the workout I suggested, that would put you at about 15-16 miles for the day, about 4.5 or so of which is quick. It's aerobically equivalent to running 22-23 miles EZ, but there is less pounding.
Your first workout or two may be a bit less volume than the above, but by the third workout you should be able to handle the above quite well. The key is doing a COMBO every 5 days and then running slow distance work between the two. Let your body absorb the harder work loads with the slower paced running between. IF you push the pace on the runs between the key workouts you'll feel tired and weak during your key workouts. The last key workout before your 10k race should be a bit easier than the preceding workouts!