Mine took over 12 hrs...
A user showed me a time ago a screen shot with FET finishing after 48 hours (I think, or 44 hours, not sure). The computer was a good one, about 2 GHz or a bit less, I think.
Also, the samples from Romania/Faculty-Econ-Timisoara-difficult take long, the last two - the ones from 2009-2010 - take longest and possibly sometimes they don't solve even after 12 hours on my computer (which is a powerful dual core 2.1 GHz). Maybe in some cases they don't solve, for some random seeds (but I know that there are also some files which solve after 1 minute or after 5 hours - like "Romania Oradea FS difficult" and "Namibia Bobby set 2 CONCORDIA").
PS: I advice you to keep the random seed at the start of generation, so that you can replicate the generation process on your computer or on other computer.
Edited to add: consider that you may need to keep the same FET version to replicate a result with the same random seed, as from one FET version to another the algorithm may change a bit (as happened in FET-5.14.2, from FET-5.14.1).