Archived:Plitvice Lakes
http://www.np-plitvicka-jezera.hr/en/
In March, the opening hours are 8am to probably 6pm (depending on when Spring starts - if late March still counts as "Winter", then 4pm)
Probably only entrance 1 is open.
Parking is 7kn/hr. That's about 80p.
Park tickets are 80kn each, which is about £9. This includes use of the bus service and boat taxi, which is nice.
We are arriving from Split, which is ~250km by road, Google says 3 hours down the coast, 3.5 overland. We're departing for Trieste, another 3.5 hours. (We should stop in Rijeka for dinner. Which leaves something like 4-5 hours for the lakes.
We'll probably want to check the bus and boat timetables when we get there, but there is plenty of scope to work out a sensible route for the time available.