"Many people need up to 10 hours sleep a day, although a few need only five".
The whole sentence is not natural and wrong. Forget about countable and uncountable nouns this is confusing you and others in this sentence.
you need to reverse the structure to be naturally fluent.
First serious error, you start the sentence wrong with ALTHOUGH, but you have not yet given as anything to compare with.
( first statement, followed by ALTHOUGH, SECOND STATEMENT).