Set time as “Busy” in an Exchange calendar without creating an appointment/meeting

You have a mismatch of your timezone settings between your Google calendar and Windows. Check in your clock settings that your timezone is actually set to the correct one for your location. Then check your timezone settings for Google calendar. Have a look at this article for a guide.

Assuming your server is Exchange 2007 or above then you can configure a resource mailbox to automatically accept meetings.

Technet

Use the Calendar Settings tab to modify the Calendar Attendant settings for this mailbox. The Calendar Attendant processes meeting requests as they come in, even if users are not currently logged on by means of a client such as Outlook. Meetings are automatically placed on the calendar as "Tentative" so timeslots won't be overbooked. You can use the Calendar Attendant to accept and decline requests for users.

• Enable the Calendar attendant Select this check box to enable the Calendar Attendant or clear the check box to disable it. It is enabled by default. When Calendar Attendant is enabled, the following settings are made available:

• Remove meeting forward notifications to the Deleted Items folder If you select this check box, meeting forwarding notifications are moved to the Deleted Items folder after they are processed by the Calendar Attendant. This setting is disabled by default.

• Remove old meeting requests and responses If you select this check box, the Calendar Attendant removes old and redundant updates and responses. This setting is enabled by default.

• Mark new meeting requests as Tentative If you select this check box, incoming meeting requests are marked as "Tentative" on the calendar. If you don't select this check box, pending requests are marked as "Free". This setting is enabled by default.

• Process meeting requests and responses originating outside the Exchange organization If you select this check box, the Calendar Attendant will process meeting requests that originate outside the Exchange organization. This setting is disabled by default.