Consuming All Calories Before 1PM??

You are likely just playing with water weight/glycogen stores and the amount of food/waste in your stomach

Does the weight stay off?

When do you weigh in? If you stop eating at 1pm and weigh yourself the following morning then you should be lighter since your body has used up all the stored food energy and your belly is empty.

I'm assuming you weigh yourself sometime in the early morning. If you finish eating at 1pm and weigh yourself at 6am your food has worked its way through your system and you have less in your stomach then you would if you finished eating at 6pm.

So does that mean it isn't actual weight loss? I'm trying to understand the process and why eating early affects me that way.

No, it is not actual weight loss. Any number of factors affect scale weight. Things like undigested food and waste can affect weight. Since you stopped eating much earlier, more of the food would have made its way through your digestive tract. I am assuming you weight after you go to the washroom.
The other part that I was talking about is glycogen store. Glycogen requires water to be stored in your muscles, it is the source of energy your muscles use. As you deplete your glycogen stores, you also release the water stored in the muscles. Think of it as a fuel tank. SInce you last eat at 1 pm, and continue to use glycogen, your weight goes down slightly. Once you eat, those stores are replenished, and the weight goes back up slightly. This is also what happens when people cut carbs drastically and drop 10 lbs (and why people post panicked questions when they "cheat" on a low carb plan, eat some carbs and spike up in weight). It is merely water weight, not fat loss.

Basically, today was very unhealthy and high-sugar. It looked like:

6:30 AM 1 muffin w/ butter, some grapes and figs

8:30 AM waffle, blueberries, peanut butter

12:00 PM spinach salad, small piece of garlic bread, frozen yogurt, fruit, chocolate chips

The total ended up a little under 1900 calories.

Not sure how this would add up to 1900 calories. Very little protein so I'm sure you aren't hitting your macros.

Unhealthy, unrealistic.

The only thing on your menu you posted that I saw that was 'bad' was the muffin with butter.

You don't give any info on your activity throughout the day. You could be consuming 1900 calories before 1pm and burning 700 after.

Get rid of the scale, seriously. You seem to be obsessed over it. I was the same way and stopped using it entirely. At your weight it's not important if you weigh 135 or 132.3. You're at a healthy range unless you're like 4 feet tall.

Just eat healthy and burn calories. That's all it is about.

I'm assuming you weigh yourself sometime in the early morning. If you finish eating at 1pm and weigh yourself at 6am your food has worked its way through your system and you have less in your stomach then you would if you finished eating at 6pm.

So does that mean it isn't actual weight loss? I'm trying to understand the process and why eating early affects me that way.

No, it is not actual weight loss. Any number of factors affect scale weight. Things like undigested food and waste can affect weight. Since you stopped eating much earlier, more of the food would have made its way through your digestive tract. I am assuming you weight after you go to the washroom.
The other part that I was talking about is glycogen store. Glycogen requires water to be stored in your muscles, it is the source of energy your muscles use. As you deplete your glycogen stores, you also release the water stored in the muscles. Think of it as a fuel tank. SInce you last eat at 1 pm, and continue to use glycogen, your weight goes down slightly. Once you eat, those stores are replenished, and the weight goes back up slightly. This is also what happens when people cut carbs drastically and drop 10 lbs (and why people post panicked questions when they "cheat" on a low carb plan, eat some carbs and spike up in weight). It is merely water weight, not fat loss.

That makes sense to me. It's just that I've sort of been waiting to drop those couple random pounds I gained this week, so I assumed when I woke up a pound lighter that my body was just getting on board with my healthy habits. But your explanation makes more logical sense by far.

I've noticed that when I quickly gain a few pounds (in a few days) the gain is usually just water weight too and will normally come off really quickly!
Last week, I weighed 135 pounds up from 125 (due to eating whatever I wanted for days in a row and having my period). 3-4 days later and I'm down to 126.5! So the gain was really just extra water weight from too much sodium most likely!

I like to weigh often too, but if you weigh everyday, you can not put too much stock in your weight or its fluctuations. It's normal to have a 5lb range that your weight will fluctuate around, depending on what you've eaten, the time of day, how much sodium you've had, etc.!