Even in the able-bodied version, biathlon and nordic skiing (aside from the sprint event & relay) have staggered starts, so some racers start 15 or more minutes behind the first. The athletes run against the clock, not directly against each other since the first person to start would otherwise have a massive advantage.
The extra element in the paralympic version is the disability classes. As an amputee, Masters is the least disabled class in sit-skiing, so the clock runs at 100% for her, versus a paraplegic (no hip movement or abdominal muscles) like Yang whose clock runs at 86%. In the VI classes, the people with some vision run at 99% versus 88% for the ones with no vision. The standing races have more classifications because there are so many different disabilities - in yesterday's men's standing race the three medalists were in three different classes, Wang (no arms) clocks at 90%, Daviet (missing one knee joint) at 93%, and Cai (missing one hand) at 96%. Standing gets additionally complicated because the clocks are different for skate-style versus classic style (essentially, the one-arm skiers are more impaired for classic, but the one-leg skiers are more impaired for skate).
I hope that helps a bit!