You can donate blood in a flight status. But you are down for 4 days and can not land aboard a ship for 2 months I think? Not positive on the time that you are down.
Edit here is the correct info from 3710.
8.3.2.11 Blood Donation.
Although blood
donated in small quantities is quickly replaced and does
not adversely affect ground activities, the hazards of
hypoxia and reduced barometric pressure make it
desirable to limit such donations by flight personnel in
accordance with the following:
a. Flight personnel shall not be regular blood
donors.
b. Flight personnel in combat or flying in a shipboard
environment shall not donate blood within
4 weeks prior to such flying.
c. Flight personnel shall not participate in flight
duties or perform low-pressure chamber runs for
4 days following donation of 450 cc of blood
(1 pint).