When my truck (and me) were at PBJ last year I was in the shop from opening to well past closing (usually midnight or so) with Joe.
Here are the "issues":
1) During business hours he's constantly talking to walk in potential customers to get price quotes, schedule dyno time, etc
2) He's interupted by UPS, Fed-Ex, etc
3) The phone is always ringing
You get the idea
Now mind you, when I was there he did have a helper with an extensive background from Chrysler, he would do some of the more simple jobs for Joe. Unless things have changed Joe hasnt found anyone to put the quality and time into the job like he does, its his name on the product when it goes out the door as well as his reputation.
In his interview process he lets the potential help know that if there is so much as an oil drip or any "issue" on a customers car after it leaves his shop that person who finished the project will be flying out to fix the customers car and get it done right.
He doesnt have a secretary mainly because he/she would only ask him 99.9% of the questions that he gets asked anyway on the phone, in person, etc so he isnt really saving time hiring one.
The bulk of his work (uninterupted) gets done after standard business hours when the phones dont ring, doors are closed, etc.
Trust me when I say he's busy from opening to closing and then some, he doesnt take a rest except MAYBE for lunch, I watched him and tried not talking cars and trucks with him because he loves them so much and it would only slow him down.
That was my experience from spending a week with him last year while he was working on my truck.
When I got the truck home I would call him on the phone (hoping he wasnt too busy) asking his opinion for tuning the VECIII for my elevation, he spent the time with me and I really appreciated it.