updateItem try4

 <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
    <soap:Header>
       <t:RequestServerVersion Version="Exchange2010_SP1"/>
       <t:TimeZoneContext>
          <t:TimeZoneDefinition Id="Pacific Standard Time"/>
       </t:TimeZoneContext>
    </soap:Header>
    <soap:Body>
       <m:UpdateItem ConflictResolution="AlwaysOverwrite" MessageDisposition="SaveOnly" SendMeetingInvitationsOrCancellations="SendToAllAndSaveCopy">
          <m:ItemChanges>
             <t:ItemChange>
                <t:ItemId Id="AAMkAGRjMzNmZmY5LWU3MGQtNDM3Yy04NzhkLTIwMTg1NmFhMGQwNABGAAAAAABObYYk+7J4Q7aaFHkkbfVkBwDfWJVQrwZNRp/OY9bjrUjZAAAAfj7xAAB+MrFosgBHQqrkDt0N/PWCAALNcd9DAAA=" ChangeKey="DwAAABYAAABMdkyja/VqSJV6H6Cs0yfEAAByxN63"/>
                <t:Updates>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="calendar:Start"/>
                      <t:CalendarItem>
                         <t:Start>2017-02-09T17:30:00</t:Start>
                      </t:CalendarItem>
                   </t:SetItemField>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="calendar:End"/>
                      <t:CalendarItem>
                         <t:End>2017-02-09T18:00:00</t:End>
                      </t:CalendarItem>
                   </t:SetItemField>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="item:Subject"/>
                      <t:CalendarItem>
                         <t:Subject>Kirill Varivoda Meeting</t:Subject>
                      </t:CalendarItem>
                   </t:SetItemField>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="calendar:RequiredAttendees"/>
                      <t:CalendarItem>
                         <t:RequiredAttendees>
                            <t:Attendee>
                               <t:Mailbox>
                                  <t:Name>MeetingRoom4KHA5@dataart.com</t:Name>
                                  <t:EmailAddress>MeetingRoom4KHA5@dataart.com</t:EmailAddress>
                                  <t:RoutingType>SMTP</t:RoutingType>
                               </t:Mailbox>
                            </t:Attendee>
                         </t:RequiredAttendees>
                      </t:CalendarItem>
                   </t:SetItemField>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="calendar:IsAllDayEvent"/>
                      <t:CalendarItem>
                         <t:IsAllDayEvent>false</t:IsAllDayEvent>
                      </t:CalendarItem>
                   </t:SetItemField>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="item:ReminderIsSet"/>
                      <t:CalendarItem>
                         <t:ReminderIsSet>true</t:ReminderIsSet>
                      </t:CalendarItem>
                   </t:SetItemField>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="item:ReminderMinutesBeforeStart"/>
                      <t:CalendarItem>
                         <t:ReminderMinutesBeforeStart>5</t:ReminderMinutesBeforeStart>
                      </t:CalendarItem>
                   </t:SetItemField>
                   <t:SetItemField>
                      <t:FieldURI FieldURI="calendar:Location"/>
                      <t:CalendarItem>
                         <t:Location>Meeting Room KHA 8.1</t:Location>
                      </t:CalendarItem>
                   </t:SetItemField>
                </t:Updates>
             </t:ItemChange>
          </m:ItemChanges>
       </m:UpdateItem>
    </soap:Body>
 </soap:Envelope>