with the green card card you can stay outside of USA 6months

No longer than 6 months but if possible try not to stay that amount of time

you can stay outside the us for up to 6 months

6 months

don’t stay more then 6 months.

you got the green card for permanent residency in the US which means you need to stay in the US more than outside (that's why people say no more than 6 months out of a year). the rule is if you stay outside for more than 6 months it breaks your continuos residency requirement for citizenship but you are still eligible to naturalize. if you stay outside for more than a year, you will need a reentry permit to return, break continuous residence requirement and are not eligible to naturalize. https://www.uscis.gov/policy-manual/volume-12-part-d-chapter-3#:~:text=Generally%2C%20there%20are%20two%20ways,for%201%20year%20or%20more.