Weeks, months... Consensus view is that this is slowly dividing subpopulation, resulting in the formation of next generation of memory cells and plasma cells. You should take into account, that viability of memory B cells greatly depends on T cell help (follicular helper CD4 T cells). High affinity clones of B cells will bind antigen better. Then, they will internalize antigen and present antigenic peptides bound with self MHC class II antigens more efficiently. Such "more efficient" B cells will be better supplied with cytokines and survivall stimuli from cognate antigenspecific CD4 T cells. As result, you will see clonal selection of B cells, resulting in formation of antibodies with higher affinity. Many of clones will undergo changes in the structure of immunoglobulin molecules as result of point mutations due to functioning of hypermutation mechanism. So modified clones with higher affinity also will survive better. So, clonal representation of B cells is various in different time points of immune response. In this context you can say about subsequent decrease in intensity of responses of some clones of "newly formed memory B cells".

the attached could help.

maybe