I only have one but most definitely need a break or I start to go more nutty then usual. I didn't really start to get a break until DS was older (about the 9 mnthish stage) and it was only ever a couple of hours every few weeks or so. Now it's at least once a fortnight.

At 9 mnths old DS was still feeding fairly regularly and also fed to sleep but if I timed it right I could get away for 2/3 hrs even if he would normally feed in that time it isn't a big deal for him to miss 1 feed once every few weeks for my sanity. I was lucky in that it never affected my supply either and I don't think it would