Re: 20 year old tech...
This will be fun on Ireland.
About the same fun but reversed you now have with the continent.
In case you mean on the border between Ireland and Northern Ireland:
1) It isn't a real problem, at most a bit of annoyance for daily commuters
2) The Northern Irish parliament in Belfast will declare it a devolved matter over which it has jurisdiction independent from London (and get quiet support from Brussels), so it will still be in the same time zone as Dublin
3) Dublin might be able to get an exemption so it will be in the same time zone as Brussels for about half of the year