If a person had had a green card for more than 15 years and intends to file for naturalization after returning from a trip abroad of less than 6 months do they need to wait 90 days or can they apply right away? Is a continuous in-state physical presence of 90 days what is meant by the requirement? All other eligibility requirements have been met and this individual will be applying under the five year rule.
There is a requirement that the alien have resided for at least three months in the state where the application is filed—INA §§316(a)(1), 319(a), 8 U.S.C. §§1427(a)(1), 1430(a). Residence is defined at INA §101(a)(33), 8 U.S.C. §1101(a)(33).This is three months prior to "filing" hence yes I would wait before filing. Note that it typically takes more than three months for an N-400 to be processed - -but the clock is timed from the filing. There are exceptions for military, INA section 329; persons making extraordinary contribution to national security Section 316 (f)and persons performing religious duties (INA Sec 317).
"Residence" in this case refers to your domicile. That is, you must have been permanently residing in the state where you reside for 3 months prior to filing your application for naturalization. A brief, casusal and innocent trip abroad does not interrupt your residence for this purpose.