While it would be a good idea to make it attack any creature that doesn't attack, how would that work? Let's say you have a Diamond Shield and your opponent has a Photon (1|1). I assume that the Time Vulture would then attack the Photon because it is unable to attack. On your opponent's turn, they use blessing on the Photon and it is now 4|4 and deals one damage. (It attacks now.) Does a ripple in the space-time continuum then open and swallow you and your computer, or does a raptor bite into your skull and kill you? That's where I am confused.
If it attacked only non-attacking creatures, the Time Vulture will attack the 1|1 Photon, but not the 4|4 Photon, because when it grew, he started "moving".
But that's not how the Time Vulture works, so don't be confused!
Also, to stay true to the comic (I love XKCD), it should really only affect delayed creatures. Although, from its point of view, everything is delayed. Here come those raptors...
I know, the first version attacked only delayed creatures, but i feel it was limiting (worked only with Procrastination, Stone Skin and Iridium Warden). Also, if you think about hybernating it's all about
stopping vital signs with very very low temperatures, so it's fitting.