Lying. Have you tried lying?
No really, a group of us used to have a similar “problem” with certain person(s) and arrival times.
Solution — “dear tardy person, please enjoy your own personal customised UTC offset”.
It’s perhaps a little mean, but those people who had little trouble being on time would be told the UTC + 0 start time, and “others” might need to know the UTC -0.5 to UTC -1 “start time”.
Net result: everyone arrives roughly simultaneously.
Note: the true start time most never, ever be discussed among the group, nor can how long people have been waiting be compared. Oddly, this never presents a practical issue…
For those not living in the London /Dublin time zone, please remember to adjust your time zones for your longitude. New York as an example, needs around 5 hours taken off all times.
In addition, in the infrequent cases that the organiser is one the perennially late, the offset calculation needs to be performed in reverse.
You’re welcome and here’s to your many irritation free, longer and timely get-togethers!