Should take a few seconds - maybe half a minute if the computer is slow.
You need Samsung drivers installed in the computer.
The cable has to be a data+charging cable, not just a charging cable. (I try all of them on a computer/phone combo that I j=know works, and label the "charging only" ones.)
If you're using a USB hub (thing plugged into a USB port to give you more USB ports), try plugging directly into the computer, with no hub.
There are a lot of possibilities.