What do we say,　”Ｉｔ is 10 a.m..” or “It is 2 p.m.” in Japanese?

“Gozen” means “a.m.”

“Gogo” means “p.m.”

So we say “Gozen Jyuu-ji” for “10 a.m.” and “Gogo Ni-ji” for “2 p.m.”

Please, pay attention to the words order.

In Japanese, Larger concept comes first and smaller concept last.

Thererfore, “Gozen (a.m.)/ Gogo (p.m.)” comes first and time comes last. 

We have special word for 30 minutes.

For example, we call 1 o`clock 30 minutes “Ichi-ji-han”, like one and half in English.

“Han” means “half”

However, we do not have the proper word for “Quarter”.

In English they say “Quarter past Ten” or “Quarter to Eleven”.

We simply say “Jyuu-ji-jyuu-go-hun” for 10 o`clok 15 minutes.