Seems like a lot of people struggling with the night time willpower. I struggle with it too when I'm off the diet. I struggle a lot. I don't even want to post what I weigh right now.
I also see people talking about being extra good during the day.
That's not a coincidence.
First off, forget being extra good. You can't really diet more today than usual. If you have a calories deficit of 1000 calories a day and today you have a deficit of 1200 or even 1500, it's barely noticeable. The important part is doing it every day, not doing extra good today.
Second, being extra good makes you feel like you've accomplished something. And when you accomplish something, you reward yourself. So being extra good in the daytime makes you think you can be extra bad at night.
(This is the same basic thing that derails a lot of diets - you burn off 7 pounds of water weight early on, you get proud of yourself, you commit extra extra hard, then it slows down to 1-2 lbs per week, you get bored with the slow progress but you're still excited about the 9 pounds you're down, and you reward yourself for losing almost ten pounds... then slip back into bad habits.)
Third, make your decisions while you are in control. If your bad meal time is 8 to 10, then plan for that. If you suck at controlling your decisions at night, don't make your food decisions at night. Buy foods you can eat that you'll look forward to at night. Plan meals. Give yourself clear ways to stay in structure.
Try planning a specific dinner. I have some chicken cordon bleu in the fridge, about 650 calories plus some vegetables thats going to be 750 or 800. So I need to keep myself to 700 calories at breakfast and lunch to stay under 1500, or do exercise. I'm looking forward to this dinner, so I can remind myself during the day that i'm going to have it, and having a big breakfast will derail that. Morning Fred makes much better decisions than night Fred so I can do that.
Fourth, if you don't like to feel boxed in to eating something specific at dinner, give yourself a specific structure to choose your meals. Calories. Ww points. Grams of carbs. I have this much left and no more. I'm like this when I first get home from, grocery shopping- I have so many good things in the fridge and I want all the things right now. A day or two later it's easier because I have fewer options.
Fifth, set goals. It's hard to commit to structure. This is where your goals come in. If it's ww points, then remind yourself that you have a goal of losing x pounds, you need to stick to your goal to get there, and you trust the process. If you stay within points you'll get to your goal. A lot of times, people set nebulous goals like i want to lose some weight, or set a specific goal with a specific deadline but no real plan to get there. The purpose of the plan isn't to imagine how great it would be to be back at your college weight on December 7th. The purpose is to give yourself accountability for those times you're struggling and need a reason to stay within points for the night.
Specific goals help - I want to lose 15 lbs before my high school reunion - but it can also be I can't ####### wait to be done with dieting and if I screw up tonight this is going to take even longer. Whatever motivates you best. It might help to remember that if your goal is to eat 1000 calories below maintenance every day, and you eat 1000 calories above maintenance on Friday, you're going to have to diet two more days just go get back to where you were.
Sixth, give yourself a ritual. At the end of the day, I click "complete diary" in myfitnesspal, and it says "if every day were like today then in 5 weeks you'd weigh x". It feels good to see that, and I look forward to that ritual. It might be posting here instead, and seeing 5 notifications from people who liked your post. Pick a routine that says I'm done for the day.
It's much easier to do something than to not do something. Doing something is easy. You do it and it's done. Not doing something is hard because you can successfully not do it at 8:00, 8:01, 8:02, 8:03... and then you have to not do it again at 8:04. Having a routine that says I'm done means you can do that thing - post here, click that button, whatever- and then you have done the thing.
Seventh, if all else fails, brush your teeth. It's harder to get excited about a glass of red when you just brushed.