https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=18563 --- Comment #3 from Marc Véron <veron@veron.ch> --- Specs: https://tools.ietf.org/html/rfc5545#section-3.6.1 The "DTSTART" property for a "VEVENT" specifies the inclusive start of the event. For recurring events, it also specifies the very first instance in the recurrence set. The "DTEND" property for a "VEVENT" calendar component specifies the non-inclusive end of the event. For cases where a "VEVENT" calendar component specifies a "DTSTART" property with a DATE value type but no "DTEND" nor "DURATION" property, the event's duration is taken to be one day. For cases where a "VEVENT" calendar component specifies a "DTSTART" property with a DATE-TIME value type but no "DTEND" property, the event ends on the same calendar date and time of day specified by the "DTSTART" property. This is an ics output from Koha / current master: BEGIN:VCALENDAR VERSION:2.0 PRODID:Data::ICal 0.21 BEGIN:VEVENT DESCRIPTION:Your copy of Testtitle (barcode 12345) is due back at the library today DTSTAMP:20170623T143352Z DTSTART:20170704T215900Z SUMMARY:Testtitle is due UID:issue-2@192.168.1.27 END:VEVENT END:VCALENDAR I'm in Switzerland, so DTSTART defined in UTC time is 23.59 local time (+2, daylight saving time) Import in Thunderbird calendar displays OK, it shows 04.07.2017 23:59 for Begin and for End. The event does not span to the next day. Test on https://icalendar.org/validator.html passes OK. Could it be that Outlook does not behave as expected? (see spec above: "...the event ends on the same calendar date and time of day specified by the "DTSTART" property.") -- You are receiving this mail because: You are watching all bug changes.