We did college tours on days off from HS (Jewish holidays, parent teacher days, etc) weekends, spring break, and over the summer. Sometimes colleges were in session and sometimes not. You can google X school 2020 academic calendar to find out when their breaks are. Sometimes you can tour 2 schools in 1 day (1 am and 1pm) if touring city schools (Boston, NYC, Phl, DC) it’s exhausting but doable.
She had to take off HS for revisit days in April.