In Boeing's OFT-2 mission, an Atlas V is the launch vehicle. The solid rocket booster burns out at T+ 1:35 minutes, but the boosters are jettisoned at T+ 2:40 minutes. Why are the boosters not jettisoned immediately after burnout?
The solid rocket boosters are left attached because they don't want to separate them during the phase of highest dynamic loading of the vehicle. The risk of something going wrong during this critical maneuver is just lower when the forces are lower.
It's only a few Words in the Atlas V Launch Services User's Guide on page 33:
The SRB jettison sequence is initiated after SRB burnout. SRBs 1 and 2, if applicable, are jettisoned at a predetermined time dependent upon the dynamic pressure constraint. SRBs 3, 4, and 5 are jettisoned 1.5 seconds later, if applicable.
"dependent upon a dynamic pressure constraint" are the magic words here.