We worked on the principle that after two hours he needed to go back in the crate for a long sleep, from an hour to two hours minimum. Then when he woke he went straight in the garden. For the second week or two I basically lived in the garden, as he had a bad association with hard surfaces and mats (came paper trained) and was peeing all over the kitchen unless he was in the garden. Being in the garden we had lots of freedom, and I could praise him when he peed/pooed, and then when we came in (after some result,, I Put in him his crate, sometimes I sat next to the crate on the laptop, sometimes I busied myself in the kitchen. He could see me and here me and quite often he didn't want to be in the crate, but more often he would settle down there and sleep or chew something. I would leave the room for five minutes, or ten minutes, and much longer when he was in deep sleep.
In the early days I noticed that if I sat next to him he would sleep in the crate for two hours, but if I moved at all, he would instantly wake up. So I decided to stick it out, and sit with him for the first week and we got a good association with the crate as a cosy safe place to sleep. Then I stopped sitting there and he was absolutely fine, still slept for two hours, and settled at night etc. I think you might have to create very positive vibes around him being separate from you, even if it is just a few feet away, and then build on that.
Worst for us has been the biting stage, which is still continuing till 5 months but easing off somewhat. You will find yourself putting him in his crate or engaging in play with him, just to stop the biting. Usually it is because they are wide awake OR incredibly tired...
Once our puppy was crate trained toilet and sleep wise (ie toileting outside and sleeping very well at night and for naps in the day) we never put him in the crate to play or his awake periods. We let him wander around the kitchen and hall. To start with my husband and I differed on this, I had this idea in my mind he needed to get used to staying in his crate whilst I cooked or we had supper or in fact did most things (!) but actually he was fine learnign to mooch around and do his own thing, and I think that helps later when you need to leave them in the day.
Four hours sounds a bit long to leave a 14 week old puppy though. 2 hours sleep and then what will happen when they are awake for 2 hours by themselves without someone to either take them out to the toilet or interact with them? Mine couldn't be left for four hours. Two hours if timed right (coinciding with sleep, after a good meal) and 45 mins if they are wide awake and playing in the kitchen by themselves..but not four hours. My puppy is now 20 weeks old.