Plan on eating pizza.
First off welcome to the SMF.
Now as far as your plan goes, you are confused about a few things.
You need to have your smoker a little hotter like 220 to 230 or so. Next, you want to bring it to 165, foil, then put it back into the smoker (not the cooler) until it hits 190. Now you can pull it out, wrap with towels or whatever and put into the cooler. You want it to rest for about an hour, no less than 30 minutes.
If you want to slice and serve at six, you had better be wrapped up by 5 at the latest, 4 to 4:30 would be better. That thing is five pounds so it will take a healthy eight hours to smoke. If it goes into a good stall it can take quite a bit longer. If I were you, I would have that thing in the smoker between 0500 and 0600 tomorrow. It can always rest in the cooler if it gets done sooner than planned but you won't be able to speed it up if it takes longer. There's not much worse than having everyone stand around hungry while you are still cooking.
I would also advise against opening your smoker every hour. Briskets like to be left alone and everytime you open that smoker, propane or not, you are gonna lengthen your smoke time. Is there any fat on it? If there is, score the fat with a knife and smoke it fat side up..
