The Japanese system of expressing times and durations is fairly simple. As far as specific times go (as opposed to relative times), Japanese once again resembles French more than English, as they write times kind of like "3h26m".

In simply referring to a time of day, the suffix ji is used after the hour, and the suffix fun is used after the minutes (if any). Counting the hours, the Chinese-origin numerals are used (except for 4). Note that kyuu (9) changes pronunciation when used with ji.

 1:00	ichi-ji
 2:00	ni-ji
 3:00	san-ji
 4:00	yon-ji
 5:00	go-ji
 6:00	roku-ji
 7:00	shichi-ji
 8:00	hachi-ji
 9:00	ku-ji
10:00 	juu-ji
11:00	juu-ichi-ji
12:00	juu-ni-ji
To express minutes, you suffix fun to the Chinese-origin number. Japanese minutes are more complicated, because they change pronunciation all over the place:

:01	ippun
:02	nifun
:03	sanpun
:04	yonpun
:05	gofun
:06	roppun
:07	nanafun
:08	happun
:09	kyuufun
:10	juppun

A time of day is expressed by combining these elements. For example:

3:15	san-ji juu-go-fun
8:42	hachi-ji yo-juu-ni-fun
6:33	roku-ji san-juu-sanpun

...and so forth. Adding the word gogo indicates pm, and adding gozen indicates am. Additionally, the half hour can be expressed with han (half), so...

Shichi-ji-han gozen desu.
It's 7:30 am.

An additional time-related word that is very important is goro, which means "about" when used after a numeric time. This is required because Japanese culture often considers it impolite to be too direct or exact about things. For example, when arranging to have lunch with a friend, you would probably want to say "juu-ni-ji-han goro", which would mean "about 4:30", rather than appearing to insist on a precise time.

To express a duration, such as "three hours" as opposed to "3 o'clock", you add kan after ji. When expressing a duration, it as again considered rude to be exact, so you should usually follow the expression with the word gurai, which again indicates approximation:

Watashi wa go-ji-kan gurai nemashita.
I slept for five hours.

Ni-ji-kan gurai benkyoo shimashoo, ne.
Let's study for (about) two hours, alright?