I’m a technical ignorant, but this is very simple: if these files were downloaded remotely via a remote hack, the time stamp on the various files would have had more space between them due to slower speeds via the remote connection. Instead, the time stamps on these files shows they had to be downloaded via a local connection. There’s also some evidence it was to a USB, so that, too.
What bothers me is that this is news: this is entirely obvious and I would assume any FBI or other forensic analysis would have looked for this type of metadata immediately.
It really depends on how it was downloaded - what software. The create/modified dates can remain unchanged. Any software I have ever written or used keeps the timestamps intact.
The DNC wouldn't let the FBI examine their servers. The DNC used a private company called Crowdstrike, that they already employed, to examine their servers. Crowdstrike gave the FBI a report but never shared the actual data with them. The FBI was OK with that.