That was the toughest player question I've had this campaign.  Masks of Nyarlathotep doesn't have any calender despite the fact that dates and to a minor extent phases of the moon can be important.  I should note that the days that I've marked the full moon on may not be 100% accurate.  The only one I could be positive about was early in 1926 and I tried to extrapolate from that, but obviously just counting days isn't enough.  However, it should be good enough for the players who need to worry about what kind of light there is that evening.

                              1925

      January               February               March
 S  M Tu  W Th  F  S   S  M Tu  W Th  F  S   S  M Tu  W Th  F  S
             1  2  3   1  2  3  4  5  6  7   1  2  3  4  5  6  7
 4  5  6  7  8  9 10   8  9 10 11 12 13 14   8  9 10 11 12 13 14
11 12 13 14 15 16 17  15 16 17 18 19 20 21  15 16 17 18 19 20 21
18 19 20 21 22 23 24  22 23 24 25 26 27 28  22 23 24 25 26 27 28
25 26 27 28 29 30 31                        29 30 31

       April                  May                   June
 S  M Tu  W Th  F  S   S  M Tu  W Th  F  S   S  M Tu  W Th  F  S
          1  2  3  4                  1  2      1  2  3  4  5  6
 5  6  7  8  9 10 11   3  4  5  6  7  8  9   7  8  9 10 11 12 13
12 13 14 15 16 17 18  10 11 12 13 14 15 16  14 15 16 17 18 19 20
19 20 21 22 23 24 25  17 18 19 20 21 22 23  21 22 23 24 25 26 27
26 27 28 29 30        24 25 26 27 28 29 30  28 29 30
                      31
        July                 August              September
 S  M Tu  W Th  F  S   S  M Tu  W Th  F  S   S  M Tu  W Th  F  S
          1  2  3  4                     1         1  2  3  4  5
 5  6  7  8  9 10 11   2  3  4  5  6  7  8  6  7  8  9 10 11 12
12 13 14 15 16 17 18   9 10 11 12 13 14 15  13 14 15 16 17 18 19
19 20 21 22 23 24 25  16 17 18 19 20 21 22  20 21 22 23 24 25 26
26 27 28 29 30 31     23 24 25 26 27 28 29  27 28 29 30
                      30 31
      October               November              December
 S  M Tu  W Th  F  S   S  M Tu  W Th  F  S   S  M Tu  W Th  F  S
             1  2  3   1  2  3  4  5  6  7         1  2  3  4  5
 4  5  6  7  8  9 10   8  9 10 11 12 13 14   6  7  8  9 10 11 12
11 12 13 14 15 16 17  15 16 17 18 19 20 21  13 14 15 16 17 18 19
18 19 20 21 22 23 24  22 23 24 25 26 27 28  20 21 22 23 24 25 26
25 26 27 28 29 30 31  29 30                 27 28 29 30 31

Campaign events:
January 15: Campaign starts and Elias murdered
January 16:
January 17: Elias's funeral
January 18: Visit to the Carlyle Estate
January 19: Unspecified rare books stolen from antique dealer
January 22: Disasterous raid on cult

Full Moon on these days