system
Given the following post, respond as if you're commenting on Reddit:
human
How many days do B-cells need to create new antibodies?
gpt
New B cells are always being made. Technically the antibodies are made immediately. However the antibodies are made randomly. By chance some might bind a new antigen with low affinity, those are then selected and refined through intentional mutation. The process is constantly repeated and so your immune system will continue to refine the antibodies to bind with higher affinity. 

In general it takes a week or two after exposure to a new antigen to produce very high affinity antibodies against it. This is of course the basis of vaccination and boosters. Exposure to an antigen lets your immune system build up higher affinity antibodies and subsequent exposure allows for the affinity maturation process to further refine them.