Depends on the local HD rules and/or when the venue will let you in. I see you are one county south of me so you face the same issues I do. Technically, you either prep or cook on-site, or prep and cook in a commercial kitchen, hot hold and serve on-site. I have tried to get into several events to vend in the 15-215 corridor but they wont let me set up early enough to meat at proper on-site cook times. I have done a couple local vends where I cooked at "off-site", hot held, took the smoker to the event and put the meat back on. HD inspector didnt specifically ask where I prepped and cooked, just made sure I was equipped to prep and cook on-site. If he knew the cook time for pork butt and did the math, my goose would of been cooked. Maybe he followed the dont ask, dont tell rule? I know I did.
Based on some emails with the SD county HD on some catering I have done down there they are a little more relaxed than Riv. County. Not much but a little.
Dedicated Stick Burner, Pitmaster @ All About The Q, facebook.com/itsallabouttheq KCBS CBJ