Recursively search for most recent modification

Hello all,

I'm trying to determine when the last time a file in a certain directory was modified. I don't care what file it is, I just want to know when it was last updated. So far I have

ls -aRl --full-time --sort=time

which is close. The problem is that it only sorts within folders, not within the entire directory. How can I determine when the last file was modified?

Figures. I spend an hour trying to find an answer and as soon as I post, I find it:

find . -type f -printf "%TY-%Tm-%Td %TT\n" | sort -rb

However, I don't know how to just limit it to one line. Any thoughts on that piece?

find . -type f -printf "%TY-%Tm-%Td %TT\n" | sort -rb | head -1

It's just one of those days...