How to Import old iPhoto Libraries from Time Machine Backups into Photos on a new computer

I previously owned a circa 2012 Macbook Pro. I used iPhoto to store my photos there, and Time Machine to back everything up. Fast forward to now -- I bought a Macbook Air and want to import my iPhoto library into Photos from my external hard drive, but it's not allowing me to do it. I've tried copying the library to my photos folder. I've tried simply moving the photos from the open library to a folder on my desktop, but I lose all of the metadata (like created date). I've also tried using third party programs like iPhoto Library Manager. None of it is working! Photos doesn't recognize any of the libraries as being something it can import. Please help!