In my experience with WSUSOffline v10.8, MSSE and Windows Defender sections are rarely skipped by the 'same day' rule'.
The script proceeds to download/validation most of the time, and even though WGET further checks the timestamp (size and time/date) for MSEInstall*, nis_full*, mpam-fe* and mpas-fe* and skips them when not newer than the local file, virus definitions mpam-fe* mpas-fe* are typically not skipped.
In the last few days, these downloads commenced during each script pass for w61_x64, w100_64, ofc glb, o2k7 rus, and o2k10 rus. This is further mitigated by instability of Microsoft download servers, which results in multiple retrials - and sometimes the loss of an existing definition file and the need to rerun the script again.
I looked into DownloadUpdates.cmd and the 'same day' portion for MSSE/Defender does not check the date of hashes-msse.txt and hashes-wddefs.txt, like it does for other shippable downloads, but instead checks for the date of mpam-fe* and mpas-fe* files.
This has an unfortunate side effect of making 'same day' skipping rarely employed for me, because
a) dates for virus definition files tend to lag behind the current European date, due to time zone and work hours differences (I typically run the script in the evening or late night);
b) x86 and x64 definitions are often not in sync, with x86 version lagging further behind.
While I understand the importance of keeping virus definitions up-to-date, IMHO checking once a day is more than enough for the purpose of this tool.
If that is not viable, I would at least prefer the updates to be backed up before downloading a new version, and copied over only if the download succeeds, like it happens with wsusscn2.cab.