The millisecond is optional

See: https://ccs-specs.icpc.io/2023-06/contest_api#contests and RELTIME: (-)?(h)*h:mm:ss(.uuu)?

Author: vmcj

webapp/src/Service/ExternalContestSourceService.php

@@ -701,11 +701,11 @@ protected function validateAndUpdateContest(Event $event, EventData $data): void
             $freezeHourModifier = $freezeNegative ? -1 : 1;
             $freezeInSeconds    = $freezeHourModifier * (int)$freezeData[2] * 3600
                 + 60 * (int)$freezeData[3]
-                + (double)sprintf('%d.%03d', $freezeData[4], $freezeData[5]);
+                + (double)sprintf('%d.%03d', $freezeData[4], $freezeData[5] ?? 0);
             $durationHourModifier = $durationNegative ? -1 : 1;
             $durationInSeconds    = $durationHourModifier * (int)$durationData[2] * 3600
                                     + 60 * (int)$durationData[3]
-                                    + (double)sprintf('%d.%03d', $durationData[4], $durationData[5]);
+                                    + (double)sprintf('%d.%03d', $durationData[4], $durationData[5] ?? 0);
             $freezeStartSeconds   = $durationInSeconds - $freezeInSeconds;
             $freezeHour           = floor($freezeStartSeconds / 3600);
             $freezeMinutes        = floor(($freezeStartSeconds % 3600) / 60);