The AllowNewTimeProposal element indicates whether a new meeting time can be proposed for a meeting by an attendee.
The AllowNewTimeProposal property is read-writable for the organizer's calendar item. It is read-only for meeting requests and for attendees' calendar items.
The schema that describes this element is located in the EWS virtual directory of the computer that is running MicrosoftExchange Server 2007 that has the Client Access server role installed.
Exchange Web Services does not support new time proposal messages. To get properties that are related to new time proposal messages, use extended properties.