For most workstations, and assuming you're using VSE 8.8, I suggest a scan any time of day with the below settings -
1. Below normal or low thread priority
2. Don't scan archives.
Your typical user won't even know the ODS is running. When our internal scans kick off even I don't notice when it's running.
But if archives must be scanned in your environment, then have the scan occur when users are not around else they will notice it and will surely complain.
Improving the scan of archives may get a little relief with the 5500 engine, and perhaps with Patch 3, but it should be understood that if you include archives in your scan routines then you are more interested in security than performance.
My workstation scans run at Noon (12:00-14:00 2 hour random start) on Fridays
Low priority system utilization.
I do scan inside Archives only because I do not scan in archives via OAS.
Scans typically take a few hours to run.
Daily memory/rootkit scans are run.
GTI is set to Low on both OAS and ODS.
My server scans run once a month on the 1st Sunday at 04:00 with a 14 hour randomization. So they could start Sunday 04:00-1800 in theory.
I am open to best suggestions.