My insurance provider calculates the annual rate and charges me equal monthly payments. (Even though the weightage is skewed over summer months, I pay it in monthly instalments. So no difference if i had bought my bike in winter or summer.
Check with your insurance for a quote with M1 Pius safety course, and what would be the rates after 60 days when you get the M2. In my case, there was not a huge difference. So you might actually be able to buy a motorcycle now rather than wait till Spring if this is the only factor.