"It is 8:18 right now."
It's sort of optional. Using the particle is proper, but people drop in it casual speech since it's usually clear what you mean. Using the particle in this case also kind of emphasises "now", so it's like the difference between "it is x o clock right now!" and "it's x o clock now"
As I understand it, it is similar to Chinese. For numbers bigger than 10 you go in descending order with a size suffix.
E.g. Five hundred and thirty two (532) would be: 五百三十二 or literally 5x100, 3x10, 2. If there is a zero in the middle you just skip the value and suffix, e.g. 502 would be 五百二. If the designator is one then you just use the size suffix, e.g. 12 十二 or 100 百.