The grace period begins immediately after you installed Office 2010 on your master PC. However, it might be difficult to activate Office 2010 during the grace period if you deploy a pre-installed Office with an OS image. Either way shouldn't be doable within 25 days after the installation. You can use the latest version of the Key Management Host (KMS) or activate Office 2010 with VAMT. You can just imagine how many helpdesk calls it will provoke if you don't ensure that Office 2010 has been activated during this grace period. However, Office will start nagging users with messages after 25 days.
Volume editions of Office 2010 don't have an RFM. In RFM Office, documents can only be viewed but not modified. Retail versions of Office 2010 will only run in Reduced Functionality Mode (RFM) after the grace period of 30 days has been exceeded. Rearming Office 2010, that is resetting the grace period, works similar as rearming Windows. However, Office 2010 behaves a little different than Windows if it is not activated. However, compared to Office 2007 it has one major drawback: Like Vista and Windows 7, Office 2010 has to be activated. Office 2010 is certainly the best Office suite out there. This article explains how you can rearm Office 2010 and for what you need this feature.
