fetch-calendar: set start time to 6 h in the past

Only showing the current event if it started less than 6 hours in the past
should be fine. We rarely have longer events and those usually had an
announcement post anyways.

fetch-calendar.sh

@@ -7,10 +7,10 @@ OUTFILE=data/calendar.json
 # See here for uname -s outputs: https://en.wikipedia.org/wiki/Uname#Examples
 OS_TYPE=$(uname -s)
 if [ "$OS_TYPE" = "Linux" ]; then
-    START_TIME=$(date --date="-1 day" +%s) # yesterday
+    START_TIME=$(date --date="-6 hours" +%s) # now - 6 hours
     END_TIME=$(date --date="+1 month" +%s) # now + 1 month
 elif [ "$OS_TYPE" = "Darwin" ] || [ "$OS_TYPE" = "FreeBSD" ]; then
-    START_TIME=$(date -v-1d +%s) # yesterday
+    START_TIME=$(date -v-6H +%s) # now - 6 hours
     END_TIME=$(date -v+1m +%s) # now + 1 month
 else
     echo "ERROR: Unsupported OS type"