the time starts when they pick him up. if he was picked up at 5 minutes before midnight, he gets credit for a full day.
https://www.inmateaid.com/ask-the-inmate/my-husbands-probation-was-revoked-he-signed-his-papers-monday-does-his-time-start-from-that-day-or-the-day-he-gets-to-the-prison#answer
Accepted Answer Date Created: September 02,2018