@chieftainSupreme The precise dimensions of my order are pasted below, although I did have to sand one edge to get a perfect fit inside the frame.
Effectively the mirror is the precise dimensions of the monitor itself once the bezel was removed. Once I had that measurement I could cut the wood according to the same dimensions plus obviously accounting for the width of the wood itself and adding just a bit more (1/16 of an inch) to ensure that I wouldn’t have trouble getting it in. Given I had 3/4 of an inch all around interior of the frame to put the mirror and the monitor I didn’t have much fear about it falling out.
Also, sorry, I didn’t keep an official build log although I plan to build another one soon so I will for sure do that and let everyone know on here.
Mirrored Acrylic Two-Way (Customize Sizing) - Clear
1/8 (.118) inches Thick, 12-3/4 inches Wide, 21-15/16 inches Long