You should start loading carbs, fuel, electrolytes, hydrating, etc 2 or 3 days before the event. I know the article is for a marathon, but it still applies here. Gut rot is painful, trust me. We have a nutrition clinic every year during marathon training. It is explained at the clinic like this:
Your body is a race car. You start the event with a full tank of fuel. You go until your tank is nearly empty. You then start refueling, but only put in a 1/4 tank.(gel, chews. bar, whatever) Then you continue until you are nearly empty again and repeat the process until you finish the race. It takes about 10 minutes for the gel, etc to take effect. The key is to take it with enough time so the fuel kicks in before you bonk.
https://marathonhandbook.com/carb-loading/