Didnt explain someone in here before that this has to do with bitfinex running a cron-job only each hour? This job then checks if a swap ended and closes it.
If its handled that way then i think its not good. I cant even see how they will calculate it in a fair way if your swap is hold longer than both parties thought.
I think it has to be more frequently than once per hour - I've not seen longer than about 20mins.
As for calculating the returns... I keep unnecessarily close track of what I expect to receive, and calculating it as if the return is paid for the exact duration of the swap has been successful enough to predict the daily payment to within a few cents of the actual figure (and it isn't all in one direction so it also averages out over time)
So it averages out. The only downside of this would be if someone gives or takes an unusual big swap. Either the taker or the lender will have a disadvantage then. Though that might only be 1/50 of the amount.
Im not sure if the waiting time is the best strategy to lower server use.
I would prefer a more dynamic system anyway. Its not needed to only pay out once a day. Doesnt the taker have to pay instantly too? Otherwise he would be able to play with money he doesnt own anymore. It would be better if payments are moved from taker to lender at the moment the swap closes.