A new attempt to fix the ICS calendar

static/calendar.ics

@@ -24,17 +24,14 @@ RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
 END:STANDARD
 END:VTIMEZONE
 {% for termin in site.data.calendar -%}
-{% assign start_uhrzeit = termin.uhrzeit | remove: "h" | remove: "." | append: "00" -%}
-{% assign start = termin.datum | remove: "-" | append: "T" | append: start_uhrzeit -%}
+{% assign start_date = termin.datum | append: " " | append: termin.uhrzeit | date: '%s' -%}
+{% assign start = start_date | date: '%Y%m%dT%H%M%SZ' -%}
 {% if termin.dauer -%}
-{%  assign dauer = termin.dauer | times: 100 -%}
+{%  assign dauer_seconds = termin.dauer | times: 3600 -%}
 {% else -%}
-{%  assign dauer = 100 -%}
+{%  assign dauer_seconds = 3600 -%}
 {% endif -%}
-{% assign end_uhrzeit = termin.uhrzeit | remove: "h" | remove: "." | plus: dauer -%}
-{% assign dauer_tage = end_uhrzeit | divided_by: 2400 -%}
-{% assign end_uhrzeit = end_uhrzeit | modulo: 2400 -%}
-{% assign end = termin.datum | remove: "-" | plus: dauer_tage | append: "T" | append: end_uhrzeit | append: "00" -%}
+{% assign end = start_date | plus: dauer_seconds | date: '%Y%m%dT%H%M%SZ' -%}
 BEGIN:VEVENT
 UID:meeting+{{ start }}@techaachen.de
 SUMMARY:TechAachen - {{ termin.title }}