There's both a sound and visual warning - download paused, and a nice 21st century signal bar that goes down as you move away.
As for the timer, I get it, it's that scene from every space/action/spy movie... they're closing in on your position, just hold them off for a few more minutes, I'm not done copying/downloading/uploading the harddrive/noc list/virus... so ya, it has it's place, but 300 seconds....
Here's a suggestion for FDev. We can start the download, loot the nearby lockers, and then hide by the door to zap anyone who might interupt us... Or... bring back the Alpha Biological scanner game! Stay safe for 300 seconds, or focus on the data port and every pattern lock cuts 15 seconds off the download time with changes to speed & direction.