The dog needs something to do otherwise they will want your attention, if they are used to getting it constantly or want it if they fancy a play with you etc., Of course you can still play with your dog at other times, but chill times, nothing happens in between you and your dog. Not even eye contact.
Preparation is key. Prepare the Kong etc and make yourself a cuppa. Now give the Kong to the dog and he will probably take it to a place he likes to sit when enjoying something nice. Make a note of the time at this point. We need to know roughly how long it takes your dog to devour the Kong, likki mat or chew etc., This is your guaranteed chill time. Let’s say this is 10 minutes.
So, 10 minutes have passed, and your dog has finished his Kong. Does he start bothering you, whining, pacing or does he lay down still where he was enjoying the Kong? If he is still quiet, not bothering you, maybe moved away and starts to play with a toy on his own etc, keep the clock running. This is still ‘chill/entertaining himself time’. You should only stop the clock if your dog whines, barks at you, paws at you etc., all indications that he is not coping with having to entertain himself and is trying to engage you in some form of interaction with him. Then stop the clock.