Other answers are correct for blood. However, if you donate platelets or plasma, it takes longer. If you're doing platelets, the donation can take as long as two hours.
It really depends, go well hydrated, it could be 20 to 45 minutes and yes it helps to make an appointment but it is not required
It also depends on if you're doing a single or a double. If you do a singe it takes about 20 to 30 minutes and if you do a double it can take 40 to 50 minutes
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