Make an actual clock or something. That would be brilliant. Then people can actually say "Tennant o' clock." Which reminds that Tennant can be seen as "Ten"nant, coinciding with his role as the tenth Doctor. It's a pun like Ben Tennison.
Heck, you know what? Add in The War Doctor, to break the law that clocks usually have 12 hours. Eventually, the 13 hours can mess up a person's perspective of time and go into something called "wibbly wobbly confusion wunfusion."