What's the best way to oil. gut and chop or just chop everything up?

NO GUTS, they introduce bacteria...from my understanding.

Gut, chop, put in a clean glass jar. Loose lid. Wrap lid-jar junction with cloth athletic tape. Lets gas out keeps flies out. Put in direct sunlight for couple weeks. Stir thoroughly. Strain out bones. Strain with fine mesh to remove the flesh from the "soup" save the fleshy goop, very good pour bait. Filter the "soup" through regular coffee filters. The result will be a golden oil the color of clover honey, and the viscosity of five weight motor oil. The paste in the filters should be saved and added to the fleshy goop. Yield should be about 20-25%
oil/fish.
I tried pulling the oil off with a large syringe and a turkey baster, got way to much goop. The filter method would produce about eight fluid ounces over night, change the filter and let it drip.
Quart jar on bottom, filter basket with filter on top of jar, paper plate on top of filter basket for fly exclusion. Pour filter full with soup an about four hours later change filter and repeat, let sit over night. Next day after work repeat.
The finished product would work through a HD spray bottle like they sell in the garden section.

Im making fish oil from the stomachs of lake trout. Around 75% fat and stuck them into 5gallon pales. How long do you have to let it sit in the sun?

When I was down in New Mexico I had a hot box, just an outdoor closet that got very warm inside. I put a couple qts of chopped up catfish into a gallon jug and added a qt or so of chicken quarters and laid a glass from a picture frame over the top. It was dark in there so not like sun rendering but man it was hot and in a weeks time there was a grey oil with clear liquid under that full of the bones. But the cool part was on top of the grey oil was a white cream like when you make butter. A little lighter than cream cheese I was able to collect this from the top quite easily and it didn't smell like anything I had ever smelled before. The grey oil was rank and the liquid under that was putrid with all the sediment and bones, but that cream was golden. It had a twang and a good call, and I caught coyote and coon on it like nothing ever tried. I had muskrats climbing almost vertical banks to get to it and get caught some ways from the water. I kept some and used it in several lures I made as a base. Sorry back to your question of how long. Once the oil has separated and you have distinct layers you can start extracting the oil. The hotter the sooner, but giving it a few extra days won't hurt as long as you don't have to worry about it drying up on you. The main thing is keeping the flies away. If they can land on your cover they will inject there eggs into the seem of the cover and those little suckers Will find a way inside.