Why can't he.......

Understand what 'later', 'tomorrow' mean?
Is it so difficult for a dog that somehow knows it's a Sunday and it's 8 am so he needs to go look out the window because his friend is coming, to get these simple concepts?
I am guilty of talking to him regularly so he understands more English than I planned on him knowing, which means we have to spell things fairly often or risk setting off his adrenal glands and dealing with the consequences, but he sure doesn't know what 'later' or 'tomorrow' mean!
For instance he was really up my butt earlier, clearly wishing I would DO something with him ( he had an enforced rest day so had only a 1.5 mile walk this morning) so I said, "I promise tomorrow we'll have a really long walk".
All he heard was WALK!
Try telling him that he'll go in the car later and watch the spinning begin
It's kind of fascinating because he picks up so many unintentional cues and pieces them together and draws a conclusion about what I am doing next that I am surprised that he hears "walk tomorrow" and acts like it will happen immediately. He knows the sequence of events leading up to a walk and one would think that the word 'walk' without the other cues wouldn't have so much meaning to him, but it does.
Somehow I am going to work on teaching 'later' and 'tomorrow'. I am not overly hopeful of success but seeing that he has learned so much of the language on is own I figure it's worth a try.
Hmmmm not sure how to even start though