A few of the biggest issues I see with this is people not going slowly enough and not adding value to the place cot (or wherever they are saying) by rewarding them frequently on it.

People will also often recall the dog after waiting a long time and get really excited. What this does, is it makes the dog build more and more frustration on the place cot while waiting in anticipation of the explosive recall fun.

This can be beneficial for building recall, but it does not help to teach a duration down stay.

Reduce and clarify the words you use. Pay close attention to your body language and reward them often from remaining in place.

As always, have fun!