I want to say "8 'o clock in the morning".

Should I say {po 8 am}, or {8 am po} ?

(I didn't write the time in klingon for simplicity..)

Neither. Write "8 am." The am means it's morning.

In Klingon, write chorgh vatlh rep. If you can't be bothered to write it out, just write 0800.

-- 
SuStel
http://trimboli.name