if you are sincere.. you can always go to them 
National Blood Centre
The opening hours of the National Blood Centre located at Outram
Road are:
Monday to Thursday 9am to 6 pm
Friday 9 am to 8 pm
Saturday & Sunday 9 am to 2 pm
Singapore Blood Transfusion Service (SBTS) has received feedback
from donors requesting that the National Blood Centre remain opened
after office hours. With the extension of opening hours SBTS hopes
that it will be more convenient for donors to give blood after
work.
