@jamierite74 Hard to answer. Once the body adapts after a couple of weeks from maintenance to a bulk (and vice versa), and it's in a consistent surplus of energy that it can now use, you're basically maximising the speed it can build muscle.
I personally aim for 4-6 months bulk. I've just ended a bulk 2 weeks ago due to my appetite going and the fatigue of force feeding, abs looking a bit cloudy. Now I'm doing an aggressive mini cut for 4 weeks or so, maybe 5.
My plan is to do this continually. Short bulks and aggressive mini cuts to minimise the time dieting and maximise the time massing.
I wouldn't be able to do aggressive cuts if it was longer than say 6 weeks. So I'd make the argument that it's a little more optimal from a gaining perspective to do shorter bulks, because it gives you more massing time throughout the year.
If you bulk longer, you have to cut longer, and if you cut longer it has to be a smaller deficit to avoid the issues so it's just more downtime.
but to better answer your question, I'd say minimum 3 months for bulk and minimum 2 weeks for cuts. If you do the math with surplus and deficit numbers, you'll find that over the next 2 years it's all zero-sum. You can basically do whatever you like and there will be very little difference.