I have Masters degree with Distinction and Student of the Year Prize in Corrosion of Engineering Materials from Imperial College London, first degree in Chemistry from University of Central Lancashire and also did Technology, Material Science and Engineering and Mathematics from the Open University.
In areas where tattooing is not as closely monitored, people are asked to wait for 12 months to give blood after getting a tattoo. This waiting period ensures that the donor is free of any potential blood-borne diseases which could have been passed on unsanitary equipment.
I used to give blood every couple of months. It usually took between 15 min and 30min to donate. However, when you get there you will have to fill out a questionairre, talk to someone, have your blood pressure and iron levels tested (ithink that's about it). After donating you will want to stay for at least 15 min afterward.