On what exact date was JWST launched?

The James Webb Space Telescope launched on December 25, 2021.

Webb lifted off at 12:20 UTC from the Guiana Space Centre in French Guiana. Its launch vehicle was an Ariane 5 ECA rocket, flying under the mission designation VA256. The launch site and rocket were part of the European Space Agency’s contribution to the international NASA-ESA-Canadian Space Agency partnership.

The date was Christmas Day, which can cause confusion because the launch occurred on December 24 in some time zones, including parts of North and South America. The universally comparable date is December 25 in UTC, the standard used in mission records.

After launch, Webb spent about a month traveling toward the Sun–Earth L2 Lagrange point, roughly 1.5 million kilometers from Earth. It entered its operational orbit in January 2022, and its first full-color images were released to the public on July 12, 2022, following an initial release the previous day.