I think that this would be a great module to have. A timer to keep track of unique mobs spawn times on RK.

You'd have to set the timer manually the first time.
To set spawntime:
!kelly dead
To check spawntime:
!kelly
To clear spawntime:
!kelly clear

Bot would then calculate next spawn from the point when !kelly dead was set. This would be a great tool for some of the RK unique mobs. Mostly the 18h mobs like Kelly, Daria, Van Horn, Zuwadza etc.

I would make such a module if I had enough knowledge of PHP, but since I don't I was wondering if anyone would take on making this one?

Good question. I guess a database would be the best solution.