> Generallly speaking, how long the submited site would be reviewed by editors?
There is no general time between a site being suggested and it being reviewed.
> and when can we treat the submission failed if not get listed?
A suggestion is failed when you do not get the confirmation message on your screen directly after making the suggestion.
The rest is not failure. A site can be accepted (listed) or rejected. If it is rejected we just do not want to list it.
In all cases (accepted, rejected or still waiting review) there is no reason to suggest the website again.