Depends on who he mouthed off to, and how big a deal that officer made in their report. Seven days is normal. If there weren't any additional aggravating factors, my best guess would be another week... if there were it could easily be months

if he is alone in this lockdown status, then privileges like email (commissary, phone, and visitation too maybe) were evidently taken away for some disciplinary reason.

Prison/jail is no joke. Sometimes the young jits need to settle down and not get mixed up with others. The first couple isn't too bad, hopefully, he'll learn a lesson. But if not, he'll be looking at solitary before you know it.

this sounds like "diesel therapy". it is a form of punishment where inmates are shackled and then bused for days from one destination to another. It has been alleged that some inmates are deliberately sent to incorrect destinations as an exercise of diesel therapy. 

What do you think happens? I saw a cho-mo get his teeth completely broken out with a weight and then having their mouth used by the inmates repeatedly, over days until they were transferred...

there is no maximum... i knew guys that were in there for their entire bid. it really depends on the infraction and reason for being sent there... for instance, getting caught with a cell phone got one guy 9 months in the SHU another got 18 months in the SHU

This happens when an inmate breaks enough rules or has been involved in fighting or smuggling contraband where the administration will change the inmate's classification requiring them to be housed in a more secure facility with fewer freedoms and privileges. Whatever the reason, it's not a good thing for the inmate.

It's probably a bad idea. There are shakedowns happening all the time, if they find them, they will be confiscated and the inmate could face disciplinary action such as a stint in the SHU

all VERY bad if an inmate gets caught with a cell phone. Obama made it a federal crime now with a 5-year sentence added onto the original sentence (if they choose to prosecute, which is unlikely unless they prove it was used to further crimes on the outside)

you will be sent to the hole for months