Close look here didn't reveal that there is currently any expire time for suggested edits.
My request is simple: if suggested edit is not approved or rejected within 24 hours, silently ignore it as if it never existed and maybe notify the one who suggested it so that he can suggest again.
Upon one approve/reject (in SO), extend the period in another 24 hours.
Such thing can happen for edits in uncommon questions that are strictly related to code which not many are familiar with - e.g. suggesting a fix to glaring coding error in some answer, but only few can tell if it's really a fix or not.
Having such thing will help clear the queue and let new edits to be sugggested.