Backup question and options(Backup settings, space on disk, and session timeout)

[asmit157]

Sorry if this information has been covered in another post, but I couldn't find it.

First, I'm using a Linkstation Duo 2x 1TB drive NAS to backup a small office (3 users, 5 computers).  I'm running a RAID 1 configuration to ensure (to an end) reliability and data security.  Further, I'm backing up to a 1TB Stealthstation which is kept offsite in the event of a disaster.  I backup to this once a week using a complete/differential backup without encryption or compression (per Buffalo's recommendation for USB 2.0 drives).  It does include one Mac (Time Machine).

First, the weekly backup (to the USB drive) takes more than a full business day to complete which is less than ideal given that the concept is to keep this backup off-site.  This means that I end up leaving the drive overnight to complete the (271.2 GB on Linkstation) backup.  I was under the impression that this method only backs-up modified/new files.  Given the (approximate) 35 MB/s transfer speed of USB 2.0, depending on processing speed, shouldn't it be able to complete the backup within the course of an hour or two?  Are these settings truly optimal, or is there a way to decrease the time necessary for backup?

Second, the USB disk has ended up now with 326GB on disk, whereas the NAS only has 271GB.  Accounting for prior installed programming and trash on disk (trash boxes are excluded), I'm not sure how to account for this 50GB difference.  The USB drive has never been used for anything apart from this.  Does the complete/differential backup not compensate for files deleted since the prior backup, or could this be from some other source?  If it does not erase "deleted" files under these settings, how would I enable it so this doesn't end up taking a significant portion of the disk necessitating either manual removal or a complete restart of the backup process(formatting or otherwise erasing the USB disk)?

Finally, monitoring the backup at times requires me to login to the backend admin page.  There seems to be an inborn session timeout of ~20min.  How do I modify this timeout so I don't have to login 10 times a day (as I am never concerned with someone physically being at my computer while I am logged in)?