<p>Depends on the internship. If it is highly sought finance internship, then generally same day or next day, although they say that they will let you know in around 1-2 weeks. However, it took a month for one of my friends to hear back, since others rejected their offers.</p>
<p>For non-finance internships, I would say 3 days - 1 week, 2 weeks maximum.</p>