It seems as though when initiating a full backup in TFS (and of course depending on the size of your environment), TFS will report that it has successfully completed the backup even though it is not possible to complete a full backup of a 1TB database in 5 minutes:
To truly see if a backup is taking place and what its current status is one can execute the following T-SQL query in SQL Server Management Studio:
estimated_completion_time/1000 as "seconds to go",
dateadd(second,estimated_completion_time/1000, getdate()) as "estimated completion time"
FROM sys.dm_exec_requests r
CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) s
WHERE r.command in ('RESTORE DATABASE', 'BACKUP DATABASE', 'RESTORE LOG', 'BACKUP LOG')
Microsoft seem to be aware of this and have suggested that I submit feedback on this issue.