I'm not sure about Canada, but in US we have January 31st deadlines for W-2's and 1099's.  The update has to be applied before the W-2's and 1099's are produced.  Therefore, we cannot wait until AFTER January 2022.  We can do it anytime between the year end version's release and the time that W-2's and 1099's are produced.  This link may be helpful.  It looks like 20.5 will be the year end version and I haven't seen it's release yet.  Usually it is released around the middle of December.

https://support.na.sage.com/selfservice/viewdocument.do?noCount=true&externalId=21690&sliceId=1&cmd=&ViewedDocsListHelper=com.kanisa.apps.common.BaseViewedDocsListHelperImpl

Version 20.5 is scheduled to be released December 9th.  The notification is generally posted in the Sage 300 CRE Announcements, News, and Alerts section of Sage City (just in case it is not available on the 9th).

Should we do the download of 20.5 before the end of December? Or when do you recommend the download to be done?

Should we do the download of 20.5 before the end of December? Or when do you recommend the download to be done?

The update was released on the 9th.  I recommend you install it prior to generating Government Year End reports (e.g. W-2, 1099, etc.) - generally due by the end of January.  You should also run File Doctor on your data just prior to upgrading (noted in notes on the download page and upgrade instructions).