The problem is that the ICS file is using a custom timezone definition whereas JEvents looks for standard OLSEN timezone names.

We deal with these by mapping them to official timezone names.

Microsoft uses some strange naming conventions - in this case "GMT Standard Time" which adjusts for daylight savings where in the UK we read GMT to mean GMT i.e. no summer time adjustments!!

We have therefore been mapping "GMT Standard Time" to UTC (which no daylight saving adjustments) - which is consistent with https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/default-time-zones?view=windows-11

Does changing line 939 of components/com_jevents/libraries/iCalImport.php from

$wtzdata["GMT Standard Time"]                           = "UTC";

to

$wtzdata["GMT Standard Time"]                           = "Europe/London";

help?

Geriant,
Yes that has worked, awesome thanks!