About how long after liftoff did JWST separate from Ariane 5?

JWST separated from Ariane 5 about 27 minutes after liftoff—more precisely, 27 minutes 7 seconds into flight VA256. The Ariane 5 launched Webb at 12:20 UTC on 25 December 2021 from French Guiana.

Separation occurred after the rocket's upper stage had delivered the observatory onto its initial departure trajectory. Once free, Webb began its own journey toward the Sun–Earth L2 region, roughly 1.5 million kilometres from Earth. The release was a major mission milestone, but it also began one of the most intricate spacecraft deployment sequences ever attempted.

Soon afterward, Webb deployed its solar array and communications antenna. Over the following days it unfolded its tennis-court-sized, five-layer sunshield and then deployed and aligned its segmented primary mirror. These operations were commanded and monitored from Earth, with many steps designed to be adjustable if conditions required changes.

The answer is often confused with later events. Webb reached L2 on 24 January 2022, nearly a month after launch; that arrival was not the same as separation from Ariane 5.