The amount of offensive actions remaining seems to be influenced by the hits someone took in a negative way. I used all my credits at one point and didn't attack for 24 hours. My assumption is I should have a full batch of attack credits again then. Still, I was only able to do 4 attacks. I did get hit plenty of times and my Warlord's Hut even said "MINUS 7 offensive actions remaining" at one point.