While this setting is enabled (checked), events behave "as expected" and events scheduled at 10am EDT would then show at 9am CDT , 8am MDT etc.
While this setting is disabled (unchecked), events will show the same time on the event regardless of the timezone. So an event booked at 10am EDT, would show at 10am CDT, 10am MDT etc. The timezone of the calendar that is importing the ics file will set the events timezone.
Use Case for Disabling
This setting is meant to be disabled to support teams working on large time differences without time zone support. For instance: If you have two teams one based in NYC and the other in Hong Kong with a 12 hour time difference. Farmerswife currently cannot support that large a timezone difference. By setting Format and Convert Time To UTC/Zulu Timezone to disabled (unchecked) you could book work at 9am in NYC for a team member in HK. When their calendar pulls in the updated .ics information it will naturally place it on their calendar at 9am local time for Hong Kong.
Please note this is only for the external calendars. Events in FW will still show as if they're happening at the same time. This may not matter for distributed teams without overlap in their work, but it could cause conflicts or the appearance of conflicts. Second the date is the same across the board. So in my previous example, if I booked an event for 9am EDT today for a staff member in HK with the intention of them doing as soon as possible, the event would show 9am today in their local timezone which would have already happened.
Disabling Format and Convert Time To UTC/Zulu Timezone
You can disable (or enable) this setting from the toolbox in the Farmerswife Desktop Client. Select settings then web share settings from the drop down. Simply Check or Uncheck the box beside Format and Convert Time To UTC/Zulu Timezone in the Webcal section to enable (checked) or disable (unchecked)
Example of Events created with and without the Zulu Timezone flag.
This is a snippet from an .ics files showing the same event with Format and Convert Time To UTC/Zulu Timezone enabled and disabled. Notice the differences on the DTSTART and DTEND lines. This is the same event in both cases. While enabled it would enter as 10:00 am EDT and then the equivalent time in other timezones (i.e 09:00 am CDT). In the disabled event it would show as 10:00 am in whatever timezone the calendar that imports the .ics file is in.