It appears as if you can only temporarily rank someone for integer value hours on HTML5 (and mobile for this matter!)
For example, trying to tempmem someone for 5.55 hours gives them a 5 hour temp.
Giving someone a 6.66 hour tempmod gives them a 6 hour temp.
7.77 hour tempown gives them a 7 hour temp.
So on and so forth.
I've also noticed this bug on mobile, although I was told to only make a post in HTML5.