This follows on from this Microsoft Guide
http://social.technet.microsoft.com/wiki/contents/articles/7681.setting-the-adfs-timeout-for-crm-2011-internet-facing-deployments-ifd.aspx
This only seems to work on PowerShell v2.0 however. Server 2012 has v3.0 and It wouldn't accept the first Add-PSSnapin command. To get around this I ran PowerShell ISE as an Administrator and then skipped this step. Everything else works as per the guide.
You can just then type in
PS C:\Windows\system32> Set-ADFSRelyingPartyTrust -Targetname "CRM Claims Replying Party" -TokenLifeTime 720
PS C:\Windows\system32> Set-ADFSRelyingPartyTrust -Targetname "CRM External Relying Party " -TokenLifeTime 720
:)
