12 miles each way / about 40 minutes, all seasons (rain, shine, wind, snow) . . . 50% busy city - 50% not so busy suburban. I've got about 200 ft of bike lanes along my route, the rest is just on the road.
It can take me as long as 50 minutes in the winter when winds are much more severe, and the snow/ice slows me down. The issue with cycling in the winter is mostly balancing sweating too much when you're pedaling hard, and freezing because you've sweated into all your clothing when you stop at lights. Also be aware that if the place you live salts the roads a lot in the winter, your bike and components will disintegrate unless you keep a very regular cleaning/maintenance schedule.
Anything below -30 C (-22 F) gets too uncomfortable for me to ride in (also, my glasses tend to get covered in steam when I work too hard, then the steam freezes and I can't see a damned thing - kinda scary). Up to those temperatures is OK with a balaclava, glasses/goggles, gloves, heavy tights, waterproof hiking boots, wool socks, and a couple layers of sweaters with a windbreaker.