Not much time really but it is possible assuming that you are now doing around 20-25 miles per week with a long run of at least 7-8 miles. If you are doing less than that now, I would reconsider.
Suggest doing something like the follow
Week 1: 10 miles, 7 miles, 4 miles (fast pace)
Week 2: 7 miles, 7 miles, 7 miles
Week 3: 12 miles, 7 miles, 4 miles (fast pace)
Week 4: 7 miles, 7 miles, 4 miles (fast pace)
Week 5: 7 miles, 4 miles (fast pace), ... and then your half marathon
Good luck.