Hi, my DS cluster fed between 5 and 9pm for quite a long time. Personally I fed from both breasts because it's such a long time, it's easier on your breasts/back and keeps the milk supply going well. My right breast always produced more milk so I wouldn't have wanted to leave the left out at cluster feeding as it was a good opportunity to increase supply. Also if LO is falling asleep it's good to move them every now and then over a long feed to rouse them a little and help them feed more effectively. I hope this is helpfull, I know there are so called hard and fast rules to follow but I do think it's trial and error for every Mum and baby to a certain extent, I hope you find what works best for you. Well done you.
Vicki.x.