BEFORE TAKING OFF AT ATL ARPT; AN MD80 CREW REQUESTED 2 MINS SEPARATION AFTER A B757 DEP.

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ATC FACILITY: ATL TWR. LOCATION: RWY 8R. WE WERE SEQUENCED FOR TKOF BEHIND A B757 WHICH WAS FOLLOWING AN L1011. ATIS RPTED NO SIGNIFICANT WINDS AND WITH CLOUDS AT 300 FT AND RPTED VISIBILITY AT 1 1/2 MI I ELECTED; IN THE INTEREST OF SAFETY; TO TAKE THE 2 MIN SEPARATION BEHIND THE B757. TWR CLRED US INTO POS AND HOLD RWY 8R. THE FO ADVISED THE CTLR THAT WE NEEDED THE 2 MINS FOR SEPARATION. NO RESPONSE. 1 MIN AFTER THE B757 STARTED HIS TKOF ROLL; WE WERE CLRED FOR TKOF. I ADVISED THE CTLR THAT WE NEEDED 1 MIN. AFTER A SHORT MOMENT; A DIFFERENT CTLR INDICATED THAT WE HAD TO TAKE OFF OR CLR THE RWY. AS I CLRED THE RWY; I ADVISED HIM THAT WE HAD TOLD THE OTHER CTLR THAT WE NEEDED 2 MINS PRIOR TO TAKING THE RWY. HE THEN STATED 'WE DON'T DO 2 MINS HERE.' IT IS MY UNDERSTANDING THAT I MAY REQUEST 2 MINS WHEN I DEEM IT NECESSARY. HAVE THE RULES CHANGED; OR IS ATL JUST PUSHING MARGINS? I DO NOT BELIEVE THE INITIAL TKOF CLRNC WOULD HAVE PROVIDED THE MINIMUM TKOF SEPARATION; MUCH LESS WHAT I DEEMED APPROPRIATE FOR THE GIVEN CONDITIONS. SAFETY CAN ONLY BE PUSHED SO FAR IN AN ATTEMPT TO FACILITATE DEPS.