=sumif("A1:A5",""&E12,"B1:B5")

is the answer to the first part

however if you are attempting to set an upper and lower bound on the
date range (ie 2 sumif criteria) you'll need something like the
following array formula:

{=sum(if(A1:A5E12,1,0)*if(A1:A5<E11,1,0)*B1:B5)}

HTH