Comparison video of how new dog reacted one of the first times being left alone (for 10mins) and how he did (for 2hrs) after some training.

I waited outside and if he stopped crying for even a second I went back inside and gave a treat.
Very gradually increased the time he had to be quiet before going back inside. 5 seconds, 10 seconds, 30 seconds etc.
If he cried the timer restarted.
I only come back when he is quiet.