5 days in dubrovnik and I want to see plitvice

Here is the Dbv bus station website, http://www.libertasdubrovnik.com/voznired.swf, which lists a one daily evening departure for Plitvice (or you could take a morning bus to Split and get a bus from there, search timetables at http://www.ak-split.hr/EN/vozni.red.)
Please note these times are subject to change.
You're looking at least one overnight there with little time to see the park if you have to get back to Dbv within 5 days. Is that what you're asking?

Thanks. Yes, exactly. An alternative would be to stay in Split, I guess. But I hear Dubrovnik is the place to go. Seems like it would be a shame to travel to Croatia without seeing Plitvice, though.

Could you fly into Dubrovnik and out of Zagreb (or vice versa)? That would save a lot of backtracking as Plitvice is only a couple of hours from Zagreb. Plitvice is about 10 hours by bus from Dubrovnik so if you have to return there you're looking at 20 hours on buses. Also note that the 1800 bus Veta mentioned arrives in Plitvice at the rather horrible hour of 0335 - not a nice time to be dropped at the side of the road. The return bus leaves Plitvice at 0945 and arrives at 20.30.

There's no particular need to take that direct bus, changing in Split gives you a lot more options, but even from Split Plitvice would be a long, long daytrip - I'd say too long in fact. So I guess you'd have a night in Split (the centre of Split is well worth seeing), a night in Plitvice, and the long trek back to Dubrovnik the next day.

As for Dubrovnik being the place to go - it gets quite a mixed reaction on this board. It's certainly a beautiful town, but people who visit in summer in particular are sometimes underwhelmed because of the crowds - the walled city is pretty small so it can get quite packed.

Plitvice is great but it's an open question whether it's great enough to spend 20 hours on a bus within a couple of days. There are lots of places much more easily accessible from Dubrovnik that are also worth visiting, including several of the Adriatic islands, Split, Kotor, and Mostar.

Dubrovnik to Plitvice is about 10 h with buses... so 1 night there