Student or Learner
The meeting will take place 17:00 hours onwards.
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)
Note that 17:00 hours or 5 p.m. would have been a better thread title.
5pm is suitable here.
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.