Why was the launch delayed one day?

The Crew-2 launch had been set for Thursday morning, and weather at the launchpad was favorable. But mission managers had to also take into account conditions in the Atlantic Ocean where the Crew Dragon capsule would splash down if something went wrong during launch. There, NASA and SpaceX decided, the winds and waves were too high.

The weather report for Friday morning foresees a 95 percent chance of favorable conditions at the Kennedy Space Center. Conditions in the Atlantic are predicted to be better than on Thursday.

Should Friday’s launch be postponed, SpaceX can try again on Monday.

source: nytimes.com