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I don't understand the meaning of these verses. Odysseus was talking about how he survived Charybdis, and suddenly he throw out those obscure words... :S
I am not sure about the syntax neither: is it a general construction? Then, why is the verb of the conditional clause in the indicative mode?
ἦμος . . . τῆμος -- these are correlative. "At the time of day when . . . at that time . . . "
ἀνέστη -- yes, as Markos noted, this is a gnomic aorist
"At the time of day when a man who is judging many disputes [νείκεα] of men in their prime [αἰζηῶν] seeking justice in lawsuits [δικαζομένων] gets up from the court [ἀγορῆθεν] [to go] to dinner--at that time the wooden planks appeared out of Charybdis [genitive]."