Anything greater than one is treated as plural, even if it is less than two, so 1.1 hours is correct, and so is "one and one tenth hours". A decimal fraction is treated as plural unless "of" is used, so "point eight seven hours" is correct, but it is "point eight seven of an hour". Fractions such as half, one third, etc. take the singular: half a mile; a half hour; one third of a metre, etc.
"Half hours" is possible if it refers to multiple units of half an hour: "I have 10 half hours off every week".