Sentence correction

[wannaknow]

The meeting will take place 17:00 hours onwards.

OR

The meeting will take place 5 p.m. onwards.


(which one is the right usage? does correct english permit the usage of 17:00 hours onwards)

[riquecohen]

The meeting will take place 17:00 hours onwards.

OR

The meeting will take place 5 p.m. onwards.


(which one is the right usage? does correct english permit the usage of 17:00 hours onwards)

I would say that "the meeting will take place/start at 5 p.m. There is no need to use onward as it is understood that the meeting will continue for some time.
Note that in AmE the 24-hour clock is used only in the military.

[Rover_KE]

Note that 17:00 hours or 5 p.m. would have been a better thread title.

[engr.yasir ali bhatti]

5pm is suitable here.

[emsr2d2]

The meeting will take place 17:00 hours onwards.

OR

The meeting will take place 5 p.m. onwards.


(which one is the right usage? does correct english permit the usage of 17:00 hours onwards)

The meeting will take place at 5pm / 1700hrs.
The meeting will take place from 5pm / 1700hrs.

In my opinion you need a preposition before the time and I agree with the others that "onwards" is unnecessary. I prefer "at".

The 24 hour clock is used in British English though not by everyone. The military, airport workers, transport workers etc use it a lot. It's used in industries where it's important to be able to differentiate between morning and afternoon/evening times without having to use am/pm all the time.