I did the Plank Challenge in April. I didn't do it 100% but improved so much. I missed April 29. Our power went out and I forgot!!!! The last week or so I didn't do the plank straight through. I had to take a few second break. Like the first day I had to do a 4 minute plank I did 3 minutes and took a couple second break then did 1 minute. Before the challenge I probably only did a 30 second plank so I think it helped me improve.
On May 1, I did a 30 second squat. I didn't want to give up cold turkey but I was so hot and miserable that I just stopped at 30. I will try to keep up doing them a bit in May.
That's an old picture but it was the closest I had to a squat.