About 2 hours. I've got an injury and I'm about 5 stone overweight. My route is quite hilly and I carried a rucksack which felt like a tonne!
Walk to work would be great. You'll get quicker and faster. Make sure ur dressed for the weather. I quite like the wind and rain! I'd recommend playing music. I wear one ear bud so I've got the nearest ear to the road free to listen out for any dangers.
Good luck!