You can do the crit simulation sessions several times a week if you want. The total ride intensity and stress is driven by the power output you choose for the 24sec segments. For example, let's say you do 6s@600W + 24s@200W repeats, you will get an AP of 280W. But, you could do 6s@600W + 54s@200W and get an AP of 220W. So, if you do a full hour of these repeats, you can get both a pretty good L4 effort and a bunch of L6 efforts.
If you don't have a power meter, your HR monitor won't be of any use because HR BPM responds too slowly. On a trainer, find two speeds or gear/cadence combinations that you can use for the acceleration segments and the cruise segments. A few trial and error sessions should allow you to refine these speeds at a constant force setting for your trainer. It's pretty easy outside. Find an empty parking lot with a row long enough for at least a 30sec cruise at 20-25mph. Coming out of the corners into the long straightaways, accelerate to 25mph in about 6secs then cruise to the next corner at ~20mph. In a race, you'll be going faster on the straightaways, but you'll be in the draft so the effort will be similar. Unfortunately, a lot of parking lots are built now with speed bumps, so you may have to cruise around to find the perfect spot.