at the risk of just diving in head first...
im assuming you are talkin about ur internet connection...if so:
then i can only assume that ur Internet Service Provider (ISP)
has a "peak time" at which your connection is reduced.
my ISP does this, but i have a 'limit' for my peak hours usage, outside of this its 'unlimited'...but i never get the full connection that i am paying for...
i guess its my fault for living so far from a server.
bring on ADSL2+