You can't join together two non-consecutive stays to make 5 nights for 5th night free but if you have a stay of, say 6 nights you can search for redemptions and then "customise" opting to pay for for any of the nights instead of redeeming and still get the 5th night free, so say you wanted to stay from 1st to 6th August you could opt to redeem 1st, 2nd August, pay for 3rd and then redeem for 4th, 5th and 6th August. Your night on 6th August would then be your 5th free redemption night.