Depends on many things - bottom line is the times vary as it can be almost right away to a few business days. Note, if your account is unverified, PayPal can hold the funds for up to 21 days.
In an ideal situation, assuming both accounts are US PayPal accounts - both the sender's account and reciever's account are "verified", neither account has any open disputes, claims or a history of returns and refunds - then the receiver would get the money almost right away.
