When's the Best Time to Do Apple Trade In Program Prior to iPhone X Pre-Orders?

[HeyGreggie]

I checked my trade in for my iPhone 7 Plus and I could stand to save about $425 courtesy of trading it in via Apple. This is my primary device, and would need it until I get the iPhone X however. My first option is to Pre-order it, but will I be able to use the trade-in option on pre-order day and get the $425 credit on that day online? Thanks guys.

Also, I am not apart of Apple's yearly trade-up program. I was just looking to exchange my iPhone 7 Plus for credit and purchase the difference in cash.