I know there are buses, but I’d really like to do the trip by train if possible.
It’s 4/12/2017 - what is the fastest train?
There are three types of trains on this route - REG (regional) and TLK ("Tanie Linie Kolejowe" - "Cheap Railways"), IC (InterCity, much more expensive usually). REG takes 2:13-2:48 hours, TLK 2:45 hours, IC 2:21 hours.
You can find all the connections on Polish railways website, on this particular day REG leaves at 03:12, 07:58, 16:30 and 20:26, the one at 16:30 being the fastest one (2:13 hours).