Keeping watch, saw Roman poet leaving right before magnate, oddly (8)
I believe the answer is:
vigilant
'keeping watch' is the definition.
'right before magnate oddly' is the wordplay.
'right' becomes 'vigil' (I can't justify this - if you can you should give a lot more credence to this answer).
'before' is a charade indicator (letters next to each other).
'oddly' indicates alternate letters (letters in odd-numbered positions).
The alternate letters of 'magnate' are 'ant'.
'vigil'+'ant'='VIGILANT'
'saw roman poet leaving' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for vigilant that I've seen before include "Ever watchful" , "On the lookout" , "Watchful, on guard" , "Carefully observant or attentive" , "Be watchful while I gilt van" .)