Nope, i couldn't find a specific answer about that.
Maybe there is not a minimum stay inside Thailand, providing you don't overstay, you don't burn your single entry (if you don't have the multientry type) or you fail to do the 90 days report or to get the re-entry permit when you leave and you renew the visa on time.
In most countries when you get a permanent resident, you are required to stay min 6 months a year or something like that, but this 1 year extension is not a real residence, just a long term permit, I am not really sure.
In my case i plan to stay about 6 months in Thailand, 6 outside but I like this visa coz i wouldn't need to do a new visa every time.