Hey don't apologize, it's why were here! Someone helped me recently so I'm just trying to pay it forward. Once all three pieces are in the smoker and it's warmed up, it doesn't make a difference on cooking time.
As for your plan, try to get your smoker going at 11AM, because it will take about 15 20 minutes to warm up; and once you put the meat in it will need 15-30 minutes fo rthe temp to rebound. That way once noon actually rolls around, your brisket has been on the smoker for 15-20 minutes and is off and running. I wouldn't wait until noon to turn on the smoker because then you are pushing 1pm by the time its warmed up and the food is cooking.
Always remember that brisket rests very nicely in a cooler so it's always better to finish early because sometimes the "stall" takes longer than you thought and you start to have a panic attack b/c it's 4:45 and you need 5 more degrees to get your finish temp and the guests are waiting.
Most likely, your brisket will be done between 3 & 4 pm. If that happens, foil it up, and plunk it in a cooler to rest. This will give you time to socialize. I know that sounds silly but I've learned that when you try to squeeze a tight smoke into a party schedule and finish the food PRECISELY at dinner time, you end up cooking the whole time and not visiting.
When its time to carve, try to save the juice from the foil, slice the meat across the grain, then pour the juice over the slices. Voila! (a little horseradish/mayo blend is always good too)
Let me know how it goes.