Time Restrictions for BW Extractions from R/3 System ??

Question

My requirement is Our Production is Server is badly overloaded & i want to restrict BW System extractions only in morning between 2.30 AM to 5.30 AM.
As BW is a sepearate team, for their different requirements they use to extract the data even in morning times also (as they feel it is urgent to them ) as they some times do not understand the slow performance is being reported by hundreds of people if it performs even for few miniutes.
I want to secure / all any RFC connection from BW system to R/3 system only in morning times @2.30AM to 5.30AM.
How can i acheive this to have complete contol on the R/3 System performance.
Rgds
PR

Answer 1

Mike Thanks for your idea !!
But i thought can we do some thing with secinfo file
As given idea - i implemented & i acheived my requirement.
I also paste the code i used for the program which may be useful for our friends
=========================================================
*& Report  ZBC_USER_LOCK_UNLOCK
REPORT  ZBC_USER_LOCK_UNLOCK.
tables:usr02.
SELECTION-SCREEN BEGIN OF  BLOCK b1 WITH FRAME TITLE text-000.
parameters : p_bname like usr02-bname,
             p_UFLAG like usr02-UFLAG.
SELECTION-SCREEN END OF   BLOCK b1.
select single * from usr02 where bname = p_bname.
if sy-subrc = 0.
usr02-uflag = p_uflag.
endif.
modify usr02."  where bname = p_bname transporting uflag.
=========================================================
Infact - i don't know ABAP  - so above small program also seems to be good & pasted here.
Rgds
PR