When I use eel i tend to give the bait upto half an hour to soak.Its tuff as hell and hard enough to pull off the hook yourself let alone worrying about pickers dealing to it.If its not been takin within half an hour then its time for a fresh bit.
Im also a fan of using cod (red) for bait.Soaking times vary depending on what part of the fish im ready to put on.I reckon the tail end half of the fillet is a little stronger and firmer and I will leave that out for upto 20mins if theres nothing biting.The fatter meatier end usually only lasts half that and needs checking more often.
The pectoral flaps I give upto half an hour.
Depending what the fish are doing and what bait im using Ill give my baits a maximum time of 20-30mins to soak before I feel the urge to freshen up.
I would easily spend half a day and more on the beach at any one time and I like to use big baits so I make sure the baits are on good and make them last.