Anything less can be interpreted as you merely taking short 'vacations' in the US, rather than making this your permanent residence.
Many people ask me, what't the shortest amount of time a person can be out of the US and lose their LPR status. My answer: 1 day.
If they quit their US job, sell their US house, take their kids out of US schools, etc. ..... they have abandoned their residence in the US.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- email@example.com -- www.capriotti.com -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
1. Do not commit any crimes.
2. Spend enough time in US not to create presumptions that you have abandoned your US residency. These presumptions may arise even if you spend less than 6 months abroad - they will look at your mode of behavior. Coming to US for a cup of coffee after a 3-month absence and then leaving again for 3 months and then repeating this pattern may very well create a presumption that you don't live here. In other words, they don't want you to use your green card as a tourist visa.
3. If you intend to travel for prolong periods of time be sure to have a travel document.