I did it in 2015, Steve Abrahams was going for his long distance challenge & hoping to ride an average of around 200 miles a day
I thought if he can do that, I've no excuse for not going out each day.
It was tough at times & my legs never got the rest they needed, as many days I was riding too fast & not taking in 'recovery' rides.
No minimum distance, though I would reckon for a GPS tracked ride it would need to be at least 0.1 miles.
I was ill for a while during the year & one day all I could manage was a ride down the lane & back which was about 0.1 mile, the shortest ride I've ever uploaded to Strava
I doubt I'll ever do the challenge again, as it may make you ride in weather conditions that are not really safe
I remember battling 50mph (ish) crosswinds, but luckily I don't think there was much ice that year, although I do recall one evening where I'd just arrived home from work one Sunday evening & my tea was ready as I walked in the door, but it was just starting to get frosty, so I got changed & straight out on the bike before it became too bad outside, when I arrived back home it was also frosty inside
Depending on the length of your ride you may need a very understanding partner
Early on in 2015 I was getting a little bit of grief, but eventually Mrs SD came round to accept it & it got to the point where she would ask what time I was riding, rather than if