The other day I heard my brother say "Set alarm for 3:15" instead of "15 minutes from now" and when I asked him why he said that latter required Google Now which required additional permissions, so he would rather figure out the time to ask for rather than accept additional permissions.

If you say "Set alarm for 7", it will do 7pm, even if you use 24 hours time. And I know no one says 19 o' clock when speaking but it is interesting.

"Set alarm for 7 tomorrow" is 7am.