How long does a contact show as "Recent"? If I send an e-mail to a contact, how long will it show as "recent"?

I wonder because when I look at one of my contacts, it has an option at the bottom of the screen that says "Remove from Recents", but I don't recall having contacted this person in over a month. This is an iPhone 6 and I also use an iPad.
I think "recents" stay in the "recents" menu until it gets pushed out by more "recents".