It's really annoying that the train service from Villa Opicina has been stripped down to almost nothing (well, it's ludicrous enough that there've barely been any trains from Trieste itself over the border for several years now). The tram is great, however!
I don't think you're in luck, though.
The websites of the local Slovene bus operator
http://www.avrigo.si and
http://www.veolia-transport.si don't turn up anything even close to that time.
I've had a look at bus times to Trieste (rather than V. Opcina) from other places in Slovenia (which could be of use if, for example, you weren't tied to coming via Sezana, but rather anywhere with a railway station), but even that has proved fruitless any later than early evening. The nearest I've found is the Veolia bus (originating from Koper/Capodistria) from kofije at 1744, which gets into Trieste at 1815 OR 1824, depending on which website you believe (you could get to kofije on a train from Ljubljana at 1720 arr 1734)
I'm sure this was mentioned in the travel columns of The Guardian in the last couple of weeks, with the recommended suggestion being to get a taxi. I can't imagine it would cost that much - given that the bus journey (Sezana-Opicina) is shown as taken only 10 minutes. Very odd that all the cross-border links have been shut down precisely now that other barriers (political and economic) between Italy and Slovenia have opened.
