Hola Miles, 

In Spanish menos = minus i.e. before the hour, and "y" = and i.e. after the hour.  Therefore, "Son las diez menos diez" is literally "ten (diez) minus ten (diez); therefore ten to ten." 

So ten to nine would be "Son las nueve menos diez," literally 9 (nueve) minus 10 (diez). 

Your phrase "Son las nueve diez" is missing a "y" and should read "Son las nueve y diez." As such it translates as "it is nine and ten" or ten past nine. 

 

Does that help? John