It will depend on the weather.
Obviously Magnolia is famous.
I live on Magnolia Rd. and today it is very nice.
Blue sky, sunny, views of snow-covered mtn peaks, light wind, decent footing, 20 degrees.
10 days ago it was -19 degrees. 2 days ago 75MPH wind gusts.
In the winter with ice and cars, and tight curves, it can be dangerous.
Plus, you'd need a rental car to get to the start.
Although, you could take the bus up to Nederland and run Mags "backwards".
All trails above 7,000 feet will be snow covered in early March.
At 5,000 feet, it all depends on the weather for the week prior.