Officials from NASA and SpaceX said final preparations were underway for a critical flight test of Crew Dragon’s launch escape system on Saturday morning from Kennedy Space Center in Florida. The four-hour launch window opens at 8am ET (13:00 UTC), and SpaceX indicated it may use much of that time to find an ideal slot due to weather conditions.

At the beginning of the launch window, weather at the pad should be ideal, but forecasters have concerns about offshore winds and waves. Later in the morning on Saturday, weather at the recovery site is expected to improve, which means the launch may well slip closer to noon than the top of the window. SpaceX may also seek to extend the window, if necessary. If the launch slips a day, conditions are reversed Sunday, with less favorable weather at the launch site but better conditions offshore.

“It’s a nice dance between launch weather, optics, winds, and waves offshore,” Mike McAleenan, launch weather officer with the Air Force’s 45th Weather Squadron, said during a briefing on Friday.