It’s not really that hard to train for pentathlon. I know that sounds ridiculous.
The old school thinking is you have to train 8 hours a day. I won’t go into how outdated that is. I coach adult athletes with jobs and professional careers and kids.
If you are already a competent rider, you will ride anywhere from daily (horse people) to 1-2x week (minimum). If you ride regularly, you really don’t need to school jumping more than once per week.
But you do have to ride intensively for long enough to achieve that basic competence. Before people go all German on me about ‘correct’ ‘every day’ training, I want to point out that if you’ve been riding and jumping regularly for say 5+ years, you don’t need to jump every day to remember how to jump. You do need to ride regularly to be riding fit.