When creating an event in the calendar on iOS (14.2) or macOS (Big Sur 11.0.1) connected via CalDav to SoGo Web Calendar, this event appears with an incorrect start and end time, it shifts forward by 29 minutes.
In the debug logs of the system, there are the correct start and end dates are received in the CalDav message:

DTSTART; TZID = Europe / Moscow: 20201203T100000 (12/03/2020 @ 10:00 am (Europe / Moscow))
DTEND; TZID = Europe / Moscow: 20201203T110000 (12/03/2020 @ 11:00 am (Europe / Moscow))

The sogo_quick_appointment table contains the values c_startdate and c_enddate in UNIXTIME format, in which there is already an offset of 29 minutes:

c_startdate = 1606980583 (12/03/2020 @ 7:29 am (UTC))
c_enddate = 1606984183 (12/03/2020 @ 8:29 am (UTC))

Logs:

2020-12-01 02:10:54.539 sogod[5800:5800] <MySQL4Channel[0x0x5598bdc5dba0] connection=0x0x5598be068190> SQL: INSERT INTO sogo_quick_appointment (c_iscycle, c_orgmail, c_uid, c_nextalarm, c_name, c_priority, c_category, c_sequence, c_folder_id, c_isallday, c_title, c_description, c_status, c_classification, c_startdate, c_component, c_partstates, c_location, c_isopaque, c_enddate) VALUES (0, '', '8A6057EC-A104-4612-AFCC-33495DB02E49', 0, '8A6057EC-A104-4612-AFCC-33495DB02E49.ics', 0, null, 0, 7, 0, 'Task01', '', 1, 0, 1606980583, 'vevent', '', '', 1, 1606984183);

2020-12-01 02:10:54.540 sogod[5800:5800] <MySQL4Channel[0x0x5598be054480] connection=0x0x5598be1d83d0> SQL: INSERT INTO sogo_store (c_content, c_folder_id, c_version, c_lastmodified, c_name, c_creationdate) VALUES ('BEGIN:VCALENDAR
PRODID:-//Apple Inc.//iOS 14.2//EN
VERSION:2.0
CALSCALE:GREGORIAN
BEGIN:VTIMEZONE
TZID:Europe/Moscow
BEGIN:STANDARD
DTSTART:20010101T000000
TZNAME:GMT+3
TZOFFSETFROM:+023017
TZOFFSETTO:+023017
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CREATED:20201201T071054Z
DTEND;TZID=Europe/Moscow:20201203T110000
DTSTAMP:20201201T071054Z
DTSTART;TZID=Europe/Moscow:20201203T100000
LAST-MODIFIED:20201201T071054Z
SEQUENCE:0
SUMMARY:Task01
TRANSP:OPAQUE
UID:8A6057EC-A104-4612-AFCC-33495DB02E49
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR', 7, 0, 1606806654, '8A6057EC-A104-4612-AFCC-33495DB02E49.ics', 1606806654);