The three years starts on the date you became a lawful permanent resident and includes any time as a conditional resident. You calculate the three-year period using the resident since date on your green card. The 18 months is total during the past 3 years. It does not need to be consecutive. However, absences of six months do cause a problem.
I agree with my colleague. You should consult an attorney if you have extended absences.
The above information does not constitute legal advice, and is intended only as general information. You should speak with an attorney to discuss your individual case, as not all facts are known at this time.
I agree with my colleague: 1) the 2 years of conditional residence is counted in the three years, and 2) the 18 months must not be consecutive however long periods of time outside of the US could be considered abandonment of your lawful permanent residency. You don't want to have a gap of 6 months.
The three years start from the day she received her conditional residence. It is not immigrant prison. Vacations are OK.
You should really speak with an immigration lawyer. Naturalization is scrutinized very intensely and problems that were overlooked during previous petitions are often discovered and create problems.
I'm intrigued by your question about immigration prison. I'm not entirely sure what you're asking, but let me take a guess.
Are you saying that you have been a green card holder for the past 3 years, but that during those three years, you spent some of that time in immigration detention? And you're wondering whether the immigration detention disrupted your period of required physical presence in the U.S?
The answer to that would be no, assuming that the detention facility was in the U.S.
However, if you were separated from your spouse by that period of detention, then you might not qualify for the 3 year naturalization provision. In general, a naturalization applicant must wait 5 years as a green card holder before seeking citizenship. An exception is made for those individuals who lived in "marital union" with a US citizen for three years after getting their green cards. Those individuals only have to wait 3 years. "Marital union" means not only that you're married, but that you're sharing a residence with that spouse.
So, if you were separated from your spouse for big chunks of time in the three years since you got your green card, you might not qualify for the exception. Now, some periods of involuntary separation can be excused--and if this is indeed the issue in your case, then you are going to want to explore those exceptions in more detail to see if they apply to you.
But maybe I've completely misunderstood the nature of your question. What did you mean when you wrote, "Like immigration prison?"?