I just ordered 3 gigs and did not notice the delivery time was 24 hours for each gig.
My mistake, it cannot be done in so short a time. 5 days was agreed with the seller. It seems my only recourse is to cancel and start again, with extra fees no doubt.
Is there a better way?
I don’t think there is a way to officially change the due date. @radjaseotea is right, just communicate!