I have the same issue.

However, as the last Monday of the month was last week, the router should have already changed the time, but it has not, and is showing the correct time.

I think that if you have set "System time" set as "Get from the internet", and you have the correct time zone selected, the router appears to be ignoring the Daylight saving setting.

We should check tomorrow once the clocks have changed.

  @DavidR1974 

It's true the router should have changed the time with the last Monday setting.  I "played around" with all of the settings just to see what would happen.  The day changes are not saved for either the start or end dates.  It is also curious that the Running Status shows "Daylight Saving Time is off" and in another AX55 configured as an AP with the same time settings, the status is "Daylight Saving Time is on" and the AP's time jumps ahead one hour when saving the settings.  In the past, I simply changed the time zone to match the current time with DST disabled which is only a twice-a-year operation.  As you stated, everything should be fine tomorrow.

  @DavidR1974 

Just did another quick test.  If you change the default day from Monday to any other day except Sunday, the day change is saved correctly and the time is set ahead one hour after saving the change and the status shows DST as on.  Later, after changing to various days and then changing back to Monday, the time is set ahead as well when saving.  Finally, after selecting Sunday, the time is in fact set back to normal and the status shows DST is off.  Therefore the router is accepting the Sunday change with the only bug being that the display shows Monday instead of Sunday.

The above is true for both the wireless router and access point modes.

Checked the router this morning, and the time changed.