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].”