First of all, glad you are listening, those are great podcasts thus far.
I believe that is older. In general, opting for either lower or higher intensity is better.
I copy and pasted a summary of Prez and Venom's article below:
Summary of Concurrent Training Principles
Modality – Cycling is preffered over running
Intensity – Bodybuilders should perform either very low intensity endurance training (>50 % VO2max) or very high intensity sprints (20X20 second sprints). If performing more traditional cardio, there will be less decraments with moderate intensity (65 % heart rate max) moderate duration (30-60 minutes) as compared to high intensity ( >90 % Heart rate max) intervals lasting 4-6 minutes in duration.
Sequencing – In general for trained individuals cardio should be separated from leg days by at least 24 hours prior to and after the training session. For untrained individuals who have difficulty putting on size 24 hours before, and up to 72 hours after should be the optimal prescription. However, if body fat loss is a priority, then they should still wait 24 hours following training.
Maximum HIIT sessions depends on how well you recover and how many times you are hitting legs with resistance training. Keep in mind that during a fat loss phase, recover will be impeded. Assuming 2 legs sessions, you could probably get away with 2 HIIT sessions.
For example, here is a sample split:
Monday - legs
Tuesday - upperbody
Wednesday - HIIT
Thursday - delts/arms
Friday - Legs (lighter)
Saturday - upoerbody and HIIT
Sunday - Off
Regarding maximal time, I wouldn't look at it that way. During a fat loss phase, you want to milk each phase for as much as it is worth. You want to get the most out of as little cardio as possible. In fact, if you are losing fat with just dietary changes, than do that, and when you stall, then add in a bit of cardio. The key factor in HIIT is intensity. You cannot do TRUE HIIT for a long period of time (as the podcast mentioned). As little as 5 minutes can be very effective (15 second sprint followed by 45 second rest, repeat 4 more times).
I personally wouldn't periodize. But if you wanted to, I think a simple way would be to start with a set amount of sprints.
let's use: 5 sprints x 10 seconds, 60 second rest. On week 2, decrease rest time by 15 seconds and on week 3 add 5 more seconds to the sprint time. On week 4, go back to 10 seconds and 60 second rest but add in another sprint.
It would look like this:
Week 1 - 5 sprints x 10 seconds, 60 second rest
Week 2 - 5 sprints x 10 seconds, 45 second rest
Week 3 - 5 sprints x 15 seconds, 45 second rest
Week 4 - 6 sprints x 10 seconds, 60 second rest