Irish indoor 400m champion Shauna Cannon gives a good interview here:
http://www.therunningreview.com/2013/12/11/athlete-qa-shauna-cannon/
In it she makes several references to the fact she incorporates long runs of 30-45 minutes into her winter training.
The 400m has long been an area of debate regarding short to long or long to short approaches. Which do you believe to be the best method? What specific benefits can be gained from running long and slow during the winter for a 400m runner? Is there value to being able to run a good 800m, or is it far more important to be able to put together a strong 200m?