I think under the circumstances, Columbo is basically saying that he will talk to the DA about settling on reducing the charges to "Assault 3" and then indicates that such a reduced charge would usually mean that time served would be "approximately around 30 days".
That's the way I take it, anywho.
Oh, and "worst episode"? One of the worst, yes. I would have to guess you haven't seen the episode, "No Time To Diet Dr. Pepper".
I sat throught this episode last weekend and although Peter Falk obviously enjoyed the aspect of adopting various disguises and personalities, the episode couldn't deviate from the old Columbo formula much more than it did.
I liked the plot set-up, but there was no pace or substance therafter and the characters are basically very cardboad.
The murderer's identity is unsurprising also, but the epsiode does have it's merits, although it's a long way from the quality of the original series.