No, no set time - he doesn't seem ready to stop now, so as far as I'm concerned, he can keep doing it
When DS was born, getting to the next feed was hard enough to think about! So I decided that if I was still finding it hard at six weeks, I'd reevaluate it. I wasn't, it had all settled down (sore nipples, lumpy boobs, fretful cluster feeding, etc). Then I went through a rough patch again when he went through a massive growth spurt, but wasn't eating much in the way of solids when I went back to work part-time when he was just over six months old. I expressed for him, I gave myself another couple of weeks, and it all worked out fine.
Now, I'm increasing my hours at work so I do three ten-hour days. It may be he goes off breastfeeding - or he may not. If he does, so be it - if he doesn't, I'll keep feeding him.
I find that being laid-back produces the same, if not better, results as knickers-in-a-twist-ness does, hence my approach to all things parenting Except whole grapes. I'm very vigilant about whole grapes