I think confusion arises because the clocks change at exactly the same moment (01:00 UTC) in Central Europe as in UK and Ireland.
As local time in Central Europe is always 1 hour ahead of UK and Ireland, the clocks change at different *local* times.
So in Ireland and the UK,
In Winter, this time zone uses UTC.
So DST starts on the last Sunday in March at 01:00 local time. The wall clocks spring forward 1 hour.
In Summer, this time zone uses UTC+1:00
So DST ends on the last Sunday in October at 02:00 local time. The wall clocks fall back one hour.
And in Central Europe
In Winter, this time zone uses UTC+1:00.
So DST starts on the last Sunday in March at 02:00 local time. The wall clocks spring forward 1 hour.
In Summer, this time zone uses UTC+2:00
So DST ends on the last Sunday in October at 03:00 local time. The wall clocks fall back one hour.
Testing shows that in Asus-WRT the "5th" Sunday works reliably, even when there are only 4 Sundays in the month of the change.