Pilot reported receiving a runway crossing clearance while another aircraft was on take off roll and had yet to pass the crossing intersection.

Narrative

We had landed Runway 28. Crossed 27L and was holding short of 27R; note it being the long Runway in Atlanta. It was a very busy day; especially with deicing. After a plane was cleared for takeoff on 27R; it lifted off somewhere halfway down the Runway or before. Before the plane was barely off the ground; still not far down the Runway; were cleared to cross at intersection T. I read it back; scanned the Runway and noticed the plane taking off had just lifted off; 100-200 ft.; maybe; and was still not even close to our intersection; maybe S or U intersection; taking off west. I hit the breaks after we passed the hold short line seeing this. The captain inquired and I said 'it hasn't crossed yet'. After what felt like 5-7 seconds it passed and we continued without incident. In the moment I believed this compromised safety and possibly was a Runway incursion because the plane taking off had not passed us yet. I believe the pace Atlanta needed to keep up with to get planes moving caused this premature clearance to cross. They were telling planes to read back call signs only; which I didn't hear until after the clearance was given. I would probably scan before starting aircraft movement and keep my attention on the radio to keep better situational awareness.