We had a long discussion on this topic in
this thread.
There are two relevant requirements (plus a bunch of other requirements that we don't need to discuss here). The first is that you must have been living "in valid marital union" with a US Citizen spouse for
three full years as of the date of filing the application. The second is that you must have been living in the US continuously after having been admitted as a lawful permanent resident for 3 years less 90 days (about two years and nine months).
If you were married and living together for at least three months before the alien became a LPR, then you'll clearly and easily meet the "three years living together with USC spouse" requirement before you meet the continuous residence requirement, so the continuous residence requirement is the critical one, the last one to be met. That's the case for most people who gained LPR status through adjustment of status.
If you were married but not living together until the alien entered the US on a CR-1 visa and gained LPR status, then two years and nine months later, it's clear that you meet the continuous residence requirement, but it's not so clear that you meet the "three years living together in valid marital union with a USC" requirement. You can read the discussion in the other thread, but I'm still not completely sure of the answer.