Hello

My father-in-law is a greencard holder. He wants to stay out of USA 6
months of every year until citizenship eligibility. Is that possible?

Also, when he called the BCIS, they said he could stay for 6 months
every year out of the country. Whereas when I called them
(800-375-5283) they said 6 months in total. Which one is correct?

Thanks for your help

There are no immigration controls when leaving the US by land. Going
into Canada, you get an immigration stamp when you first go through,
but not necessarily if you go through again within the validity period
of the first entry. They don't even swipe your passport through the
scanner. So where is the record of how long a Green Card holder has
been physically present in the US? Just curious.