CRJ-900 First Officer reported encountering strong wake turbulence departing ATL in trail of a B757; expressing concern that the spacing; while legal; was a factor in the encounter.

Narrative

ATL ATC gave a flow time to ZZZ which was within a couple minutes of the time assigned. The Captain and I completed the checklists and taxied to the runway where we were quickly told to line up and wait behind a 757. The 757 took off and when it was halfway down runway we were cleared for takeoff before the rotation of the previous departure. This may be legal for their operations but the 757 has the potential to cause a strong wake. The Captain slowly went to position for takeoff to limit the effects and I turned continuous ignition on as a precaution. After takeoff at 200 feet after the retraction of the gear we encountered a very strong burst of turbulence that forced the Captain to use full deflection of the ailerons to prevent a roll. This continued for a few hundred feet and caused us to miss the NAV mode and autopilot calls until about 1000 feet. No deviations or issues because the course was straight out for the departure. Flight continued uneventfully.Cause: Rushed clearance for takeoff followed with wake from previous departure. Suggestion: When given takeoff clearance even if it is a legal distance for ATC and our airplane; do what is necessary to ensure a safe distance behind heavier aircraft is built.