If it's at the dorms, possibly a week or so, specifically because my mom tries to check in on me once a week and got notably freaked during a period where my phone was legitimately not receiving her calls. I'm on terrible terms with my roommates so they wouldn't bother to check on me, unless one of my alarms for getting me up for class went off for hours due to me being kind of dead. I have a friend who might try to check up on me as well but it would still be a few days.
if at home, probably a day, since even though I'm a heavy sleeper my mom would catch on within the day to me not responding to her at all.