This was for a mead rather than a cider, but a couple batches I did once were done with 1/2 oz per gallon and came out very nice. I did two 1 gallon batches. One was dry hopped with Fuggle and the other with Cascade. They were both very good, but I liked the Fuggle better. I had the hops in for 5 days and then racked.
Do you know what hops you're planning to use?