What this means is that is when you can start eating towards your calories for that day. You have from 10 am until 10 am the next day to finish your 2400 calories. You can wait longer if you want, but 10 am will be your "green light". This way ensures that you will not overeat or go above a deficit. You have 24 hours to get your calories in. Get them however soon or late you want. Just remember, 10 am is your starting time, when your calorie level resets and you can start eating again.
Alot of people don`t realize they sabotage their efforts if they do not use a start time.
12 Noon is my "greenlight" but sometimes I won`t start eating until 2 pm or so, depending on how busy I am or what I am doing.
Today, I first ate around 1 PM and I still have 424 calories left. I will finish my calories up in a little while and won`t eat again until my "greenlight" which is 12 Noon.
Sometimes I finish my calories sooner, sometimes even later.