"I dimly remember seeing 24 quoted as the score for the month".
VERY dimly indeed, it seems. I've now checked and the figures given by Bill Gunston (Night Fighters, Patrick Stephens Ltd., 1976) were:
March 1941 - 22
April 1941 - 48
May 1941 (first two weeks) - 96
He also writes, "From May 11 1941 the Luftwaffe tapered off its efforts …"