If you choose a delay, the file will be deleted after that delay.
Don't worry: if a user begins to download the file before the expiration and the download ends after the expiration, he will be able to get the file.
This server sets limitations according to the file size. The expiration delay of your file will be the minimum between what you choose and the following limitations:
between 0 and 128M, the file will be kept 365 day(s).
between 128M and 1.0G, the file will be kept 30 day(s).