The refresh interval is defined in the Calendar Properties for network calendars, but if the default intervals are insufficient, it can be adjusted in Config. editor:

https://groups.google.com/d/msg/mozilla.support.thunderbird/9-zRsrdgT1s/T229Nru_FQAJ

A more complex method is linked to in this bug report:

https://bugzilla.mozilla.org/show_bug.cgi?id=1364217

Don't know why 'Calendar' doesn't appear on the tab. Try a different theme?

Thanks, but the problem isn't the frequency of the local calendar synching to the server, it is that the actual DISPLAY of the calendar isn't updating to a different range of dates when I am trying to navigate. So if I am currently viewing week starting Nov 25, and I choose the Go | Next |Week menu command, or click on the right arrow in the calendar header, or click on a different date in the mini calendar, the display won't change (it will still display the week starting Nov 25). Only by clicking on the Synchronize button will the display update to the desired new date range. For example, if I click on December 16 in the mini calendar, it still displays the week starting Nov 25, but if I then click on Synchronize, the calendar display will update to display the week starting Dec 16.

It seems I misread your question. Who is the calendar provider, and which add-on and version is syncing the calendar? Is the Accessibility box in Tools/Options/Calendar/General checked or unchecked?

I am using Lightning for the calendar functionality v6.2.9.1 in Thunderbird 60.9.1. I have various calendars, but they are pretty much either Google calendars or subscribed Google calendars, using Provider for Google calendar 4.4.2 for the syncing.

Another curiosity/diagnostic point: even when I manage to get the interface to actually display a different date range (and/or change the display mode, e.g. showing a Day instead of a Week) by hitting the Synchronize button, the gray bar at the top of the calendar still shows the original (now incorrect) date range of November 25-December 1, 2019 and the wrong CW count of 48, in other words the gray calendar bar doesn't update even when the actual calendar display does. See attached screenshot.

I'm afraid I don't have any suggestions for this problem, but you may get some answers by posting in the Issues section of the support site or in the support forum.

I'm fairly sure this is a Lightning Calendar interface/display issue, not something having to do with the Google synching interface modules. Isn't this the support forum for Thunderbird and Lightning? If not, do you know what would be the proper way to access those?

You may be right, that it's a display issue, not a sync problem, especially if it also happens with local calendars.

This is the place to ask questions about TB and Lightning, but you may have to wait before someone provides the answer. Besides the sites given above, you can try the mozillazine Calendar forum.

OK, thanks. I posted there as well. Hoping someone else will have the answer or an idea either here or there!

If you have the time and inclination, you could create a new profile with Profile Manager, install the add-on, add one network calendar, and see if the problem remains (the original profile is unaffected). This would eliminate the possibility there's something in your original profile that is causing the problem. If the problem remains, it might be hard to pin down the source. Is it Lightning, or the Provider add-on, or the OS display settings, or the display adapter? Is it fixed by upgrading to TB 68 with upgraded Lightning and Provider add-ons? For the latter, if you have another computer to install TB 68, that would keep your TB 60 setup untouched; updating and downgrading TB on the same computer is not as easy as before.