Marathon training after injury

Hi! I am training for the Houston marathon in January. I had an injury in my knee (I have defective cartilage) they said I could keep running if I do PT (i go twice a week). I had to take all of last week off and I also have missed a few runs due to it before maybe 2-3 but no long runs. I am now 6 weeks out and getting back into my training plan this week with about 50% my mileage. I am planning to still do my 16 mile run this weekend. I am worried that I will have not trained enough because of the injury. is 5-6 weeks enough time? I have gotten up to 15 miles and I am planning to do a 19-20 mile run on the 23rd, as well as my weekly lighter runs with strength training. Thoughts on if I will be able to finish/if I have enough time to continue training. Thanks!