This is a tough program for advanced athletes that have a few years of training behind them. You need to start this program having trained @ 10-12hrs a week. You should be able to swim 3km, cycle 120km and run 19km.
The HR Zones are based off Joe Friels Running and Cycling HR zones or you can use FTP or run pace.
It is best to get tested to determine these zones or you can do Joe Friels field tests: A 30min bike or run TT, get the peak 20min HR average to be used as your lactate threshold.
Strength workouts have not been included in the plan. It is highly recommended you do a strength and core program - it should be more maintenance based rather than trying to increase strength. You could do these on Tuesday and Friday (Thursday when day off on Friday). Again you should be going into this plan having done an extensive strength training program.
It is important to listen to your body, if you feel sick or extremely fatigued you should take a day or two off and do not try to make up lost training sessions, rather ease back into the program.
The swim sessions are progressive and work off threshold pace or if you use CSS(Critical Swim Speed) pace this can be applied as well. If you swim with a swim squad that is fine and certainly better to help you push yourself a bit more. Make sure the coach is aware of the race you are aiming for and when to taper and recover.