I looked into this, and checked with DFG...this is how I understand the multiday, although I'm going to preface it by the following disclaimer: call DFG in Los Alamitos and verify for yourself!!!
You are allowed to have a limit for each of the three days in possession, with the obvious qualifier that it is a one limit per calender day. You must be on the water AT LEAST 12 hours for it to count as a day ie you must leave by 11:59:59 am, and return no earlier than 12:00:01 pm for your departure and return days to count.
They MUST receive your permit application 48 hours prior to your departure, and you MUST have the signed permit, or copy thereof on your person when you are out...
You have to be a little careful about the limit thing...I found out that the salmon limit is two in possession, whether that is on your boat or your freezer...period. Not the case with lobster, I think it is three limits in possession. I don't know about WSB...
I did an overnighter (two day)...it worked out well, but I have to say, I would rather do the evening run then come home...
I said it before, but I'm going to say it again...call the DFG and make sure of your facts...
Andale