If you are interested in obtaining U.S. Citizenship as soon as possible and become a naturalized U.S. citizen, then as you receive conditional green card and enter country, you should aim to spend at least 180 days per year in the U.S. for a period of 5 years.
For Naturalization – the individual has to be physically present in the U.S. at least 50% of the time + 1 day for the last five years (so about 181 days per year). The clock for the five years of residence starts on the date of issuance of the first green card (during the conditional residence). Continuous residence is essentially that the individual does not have any trips outside of the U.S. greater than 180 days.
USCIS counts days out of the U.S. differently than we do. For USCIS, if you go on a cruise and leave Friday and come back Monday at 8:00AM, then you have been gone for four days. That is how they count, the day you left, the days in between, and the day you arrive back in the U.S.. If you have a trip out of the U.S. greater than 180 days, you are presumed to have broken your “continuous residence” for naturalization purposes.