Set an appointment for 9-10am and received an ICS file. The received an ICS file works in emClient and Outlook where Webmail is not correct. The results are below:

SmarterMail shows 4am-5am

Emclient shows 9am-10am

Outlook shows 9am-10am 

ICS File

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
CALSCALE:GREGORIAN
BEGIN:VEVENT
DTSTART:20210819T090000
DTEND:20210819T100000
SUMMARY:Strategy Session (Free- 30 Min)
DESCRIPTION:Strategy Session (Free- 30 Min)\nEric Beschinski
END:VEVENT
END:VCALENDAR

Actual ICS File