Bekka, having just had nearly all my free range hens taken by a fox in broad daylight, heads ripped off, bodies torn to shreds and left dumped around, I don't think that just turning your hens out without careful assessment of the possibilities and planning is good. They will still need to be shut in at night and will happily return to their house. Ducks don't always put themselves to bed at night though.
I suppose the answer depends totally on your local situation, in particular the local fox population. Round here the neighbour's lads used to shoot foxes so we had very few, although they always spread to fill a vacuum so freedom didn't last long. Now the lads have grown and aren't so interested in killing, so we have more foxes, badgers too, stoats, no wild mink though, but all predators of poultry.
Stereo,
The danger time for hens out at night isn't only during the night, so even if they sleep in the trees they will be down at dawn and dusk, which are traditionally the time the fox comes. Once one fox has found them they will never stop until all are gone. Not an ideal way to cull your older birds.
If hens have been used to being caged or confined all their lives, banishing them to the woods to fend for themselves does seem harsh, because they won't have a clue what to do. Also, all those carcasses will simply be supporting the local fox population. Better in my view to cull humanely and find a use for the meat.