How long should it take to see improvements in your cardiovascular system?

Hey guys, a few months ago, I started doing FB workouts on YouTube.

I was noticing that the workout I was doing, I needed to increase it every 2 weeks because it became to easy.

Now I’ve started adding high intensity exercises during rests, I increased it by 10 seconds... 2 weeks later, I increased it the rest again by 5 seconds for all body weight exercises, so it’s 50 seconds on 15 seconds rest (but again I’ve got High intensity body weight exercises like push ups and jumping Jacks)

It’s almost been 3 weeks and I’m still stuck, usually it only takes 2 weeks.

Should I continue doing what I’m doing? I’m worried that it’s stopped improving somehow.

Any help would be greatly appreciated!