Many fraternities/sororities recruit all year, and will have new members join in the fall and spring. Fall semester, however, is the time most new members join. There will be info sessions, a Go Greek! Blitz, and NPHC Meet-the-Greeks spring semester.
Some CPH sororities may continue to recruit after the fall, but this varies year to year; your only guarantee to check out every CPH sorority is to participate in fall recruitment. NPHC and non-affiliate/multicultural fraternities/sororities do recruitment or intake at their own discretion, hold their own informational meetings, but typically only take new members once a year.