Betamethasone Shot (Lung development) question...

Anyone had this shot? They want me to have it 24 hours apart. Is it a hard line within the 24 hours????

They gave me the first shot at 3pm today and then asked me to come back at 3:30pm tomorrow to miss the shift change. I should have asked but I didn't....

Do I need the second shot by 3pm????

Or does it not really matter????