@Reynaldo_Lopez We have all been there. Check out this thread and also search for Full Frontal in the forum and you will find a number of other threads in the topic.
For the 5 minute you should have some confidence about what you can hold for 5 minutes which you can get by looking at some of your MAP workouts and also your Half Monty results. From there try to push it up as much as you can without blowing up as you reach the finish.
For the 20 minute - same thing. Pace at what you are confident you can hold for 10 minutes and from there start pushing. Basically a negative split. In the second 10 minutes I try to go by RPE and also reference heart rate in relation to LTHR which you get from Half Monty.
I would also recommend the mental toughness videos. Often times adding just the right amount of positive chatter plus the right breathing will go a long way. The Tapers video has some excellent breathing techniques.
Good luck and let us know how it goes!