The standard is 1-3 days. Please understand that the prison or jail will open and inspect every piece of mail for contraband. In some cases, this delays the actual delivery to the inmate at mail call.
https://www.inmateaid.com/ask-the-inmate/how-long-does-it-take-for-the-inmate-to-receive-an-online-letter#answer
Accepted Answer Date Created: April 24,2013