Depending on how good you are with LN2, if you get the setup tuned up proper before benching on LN2 etc., you would get a few hours out of 25L, enough for a good bench session in the afternoon.
I am not the greatest at LN2 and my 50L will last me the weekend with maybe 2 bench sessions, thats why I saw 1 good session.
Now if your going AMD with max LN2 temps them 25L might be cutting it close
