How cold becomes sketchy to ride?

Got my first proper lesson booked for 8am tomorrow morning, it's not going to get above 0C until 10/11am.

Phoned the school to check they're still running it, and they said that we'll still be on but only sticking on main roads.

The rule of thumb I have been sticking to roughly is not to go out when temps are <0C or have been <-3/4c at night. Personally, if I didn't have the lesson booked tomorrow I probably wouldn't be going out, but what do people think? I'm thinking about getting the bus there but what do you all think?