It means he needs it extremely urgently. It means he wants an answer right away, and he would have preferred to have it before now (yesterday).
From Wiktionary:
Verb
need it yesterday
(idiomatic) To need something immediately or urgently; to need
something that is already late.
1972 Hearings, reports and prints of the Senate Committee on
Government Operations, U.S. G.P.O., p119 We need help - and we need it
yesterday - if local government is to remain a viable entity in our
society [...]
1980 Thomas A. Rullo, Advances in computer programming management,
Heyden, p153 Many people in systems work are so used to digging in and
getting the job done in record time (we need it yesterday!) that the
thought of taking several weeks to develop a plan before "doing"
anything might sound like heresy to them.
2006 Climate change: the "citizen's agenda", eighth report of session
2006-07, Vol. 2: Oral and written evidence, Volume 2, The Stationery
Office, p511 We need a cultural change and shift in people’s
perceptions of the concept of “progress” but we need it yesterday and
are fast running out of time.
2006 Joyce Rosenwald & Michel Bonner, The Sinclair Solution, p154
“Take care of it then,” the President shouted. “I need a summary of
the situation and I need a solution. And, I need it yesterday.”