The order of 50 would have been done by digital print, this is why 50 can be delivered by Friday.
The order of 500 will be done by offset print, which takes longer as plates have to be made. Also, standard procedure for offset printing is to provide a proof, which we send to you to review and sign off. If you don't want a printers proof to sign, then I or the printer cannot be held responsible for any error in printing. My recommendation is to provide you with printers proof for you to check and sign off. This will increase the production time.
I will get you a revised quote and timeframe for delivery. It's unlikely you will get 50 copies by Friday.