Re: "How about the d7100?"
Page 209 of D7100 User's Manual says you can use time/date-stamp if you use PictBridge. In other words, as I understand it, if you have a PictBridge compatible printer, you can connect your camera directly to the printer with a USB cable (i.e., NOT going through your computer) and then follow the directions from p.209. [I was gonna copy-and-paste that page for you here, but my computer is too slow right now to download the PDF of the User’s Manual. Sorry.]
My Epson Artisan730 printer is PictBridge compatible, but I have not yet tried to use the Time/Date-Stamp function, so that’s the best I can do you for now.
Hope that helped some. Good luck.