To answer this question, think about the goal behind using Pokermind.
It's about performing at your best level, improving your mental game and learning from the sessons to improve every day.
If you think you can do that without doing the Warmup and the Cooldown every session, fine by me.
There is no wrong way of using Pokermind.
In practice, these routines will yeld the most value when they are internalized habits, when they become a part of your routine.
Personally, I always do the Warmup and the Cooldown because I know they help me a lot. I play cash games and sessions between 90 and 120 minutes.
If you play shorter sessions and you do small breaks between them, then I would consider a block of those smaller sessions as a big session and would the routines at the beginning and the end but not during the small breaks.