First concern is...2Tbs Sodium Nitrite? If you are talking PURE then that is HIGHLY toxic. 2Tbs Cure #1 would be fine. Second, NEVER BOIL CURE! The rest ok, then cool to 40°F add Cure and meat and proceed. Three days will only penetrate about 1 to 1.5" from all sides so the center is likely uncured. Last. I would not be concerned about sitting out 10 hours in the Brine. That amount of salt, sugar and cure is inhospitable to bacteria and I would expect little if any growth, at a 70° room temp, in that short a time. If left out a couple days? Yes, spoilage would be an issue. Toxin is of no issue, in a Gallon of Brine, as any tiny amount possibly produced in 10 hours would be so dilute as to be inconsequential. Additionally we all rinse well after brining and this further removes anything that may have grown. I would remake the Brine Properly, give the pork a thorough wash, get all in the Refer and proceed based on 1 day per 1/2" thickness plus 2 days...5" thick = 12 day soak.
Guys, remember Bacteria in a brine will Eventually cause a problem but this situation is NOWHERE close to the same as a Raw Pork Loin sitting on the Counter 10 hours! You have to take ALL circumstances into consideration before telling a Newb to Toss the Meat! In the WORST situation, a plain raw mishandled piece of pork left out overnight should be tossed. But Brined or coated in a heavy amount of Rub with Salt (antibacterial), Sugar (hygroscopic binding water from use by bacteria) and Spices, (garlic, onion, chiles and black pepper, all have some antibacterial qualities)? Wash it off, re-season and get smoking, very little to no safety issue. Brines are a similar situation for these and the reasons above.
Is this info USDA approved? No...Just reality! Heck, according to the USDA, you should be tossing everything in your Refer every 3 to 5 Days going strictly by the book! Way High on the ...
...JJ