Generally, it takes 1-3 days to be received by the prison. The prison staff inspects each piece of mail for contraband which sometimes delays actual delivery to the inmate at mail call.
https://www.inmateaid.com/ask-the-inmate/when-i-use-inmateaid-to-write-to-someone-in-jail-how-long-does-it-take-for-the-letter-to-reach-the-person#answer
Accepted Answer Date Created: March 26,2013