Appending the file modified date to the file name

[Robert Moskowitz]

I am pulling a bunch of recordings off my android phone.  I found 
simple-mtpfs to be able to use 'cp -a' to actually copy the files and 
preserve their date information.

Now I want to rename these files, which are all lectures to have the 
date of creation/lastmodified in the file name.  All my searching has 
only found how to put the current date into the file name, I can'f find 
anything on using the actual file date.

Can anyone point me to how to do this?