I have done HMs 3 weeks apart, and even 2 weeks apart. 11 miles is enough of a long run for a HM.
I would run the first race, take the next week easy with about a 5-6 mile long run, then do a 10-12 long run the next weekend, and a 8-10 mile run the weekend before the race.
Of course, everyone is different, but this has worked for me in the past. I should probably mention that I mostly participate, not race hard.
Neither real food, nor exercise, come from a box.
Beat Coach Pete 5k 4/13
Gunfighter HM 6/1
Barefoot Boise 10k 9/14