I only do it when the ground can take it......I rode in the field at the weekend cos I thought it was firmer than it was....result- I trashed one of the resting paddocks
All year round generally. I dont have any choice - I have no school and don't hack! It is difficult as the ground is very rarely good. I just have to work the horse accordingly, often this means not doing any canter work for days (or if I do, only cantering up hills if the ground is too wet / slippy to do circles etc.)
I only use our fields when the ground can cope. We don't have a school, but we have excellent hacking so I manage to do most of my schooling out hacking ... and then grab the school/paddock to do more conventional work whenever possible. Usually usable pretty much from March to October except after long rains .... usable in walk through the winter.