How wonderful of you to take in a dog that had no place to go. There will be a special place in heaven for you some day!
One hour is too long at one time to try and train the pup to sit, he can't focus that long. You need to do it in smaller time periods. And if you only started training him today you need to be patient. And if your pup has never had any training at all, it will take longer than normal. As you say, he is going through a real adjustment period. Instead of training him for one hour, I would train him four times a day for 15 minutes each. Just keep at it and one day soon you will see him sit for you. Good for you for trying to train him to know the basic commands. It will make him a better dog. Congrats on your new pup!