Are they varnished?
I would stay away.
I have friends in Charente Maritime who age their mixture (pineau) in small casks (10/15 litres, I can't remember) but they keep it cool and dark in the cellar.
Also, when they start to draw they transfer the whole content to smaller Demi-johns, so that air doesn't oxidise it too quickly.
In the case of a 1 litre cask full of whisky, the amount of air would gradually increase. Try pouring yourself a whisky in the evening, and drinking it for lunch the next day...