Are you under some firewall or using VPN or something similar? I downloaded the IDE and tried to install the Edison but I got an error. I then disconnected the VPN and the download started correctly and installed the Edison in just a couple of minutes. I downloaded this file Arduino - Software
Update: tried disconnect VPN and move outside firewall still no luck (same error)... THEN I remembered I recently "downgraded" the IDE to 1.6.4 due to business needs (don't ask).
Using 1.6.5 on another computer (no VPN no firewall) - no issues.
Using 1.6.5 with VPN - same error.
So looks like it's a combination of outdated IDE and VPN issue (I'm assuming there's no incentive to retroactively fix 1.6.4 unfortunately?), so issue is resolved. Thanks