People tend to check in during these times:
Permanent Blood Donor Clinic
Come early. Gets pretty packed after 4:30 pm when all the nearby government workers want to donate. Could take +1h.
Give blood as often as you are allowed/able. It's the Canadian thiing to do!
Don't get cross with the nurses or they'll take your blood! Kidding! They'll do it anyway! Even with a smile!
Make sure they leave you enough for breathing!