Arithmetic overflow error when using DATEADD with [Timestamp] column in sys.dm_os_ring_buffers

The second parameter of DATEADD requires an expression that can be resolved to INT.  So you can't use BIGINT there.

If you are interested in delta's only, you can perhaps use a modulo operator. For example, use 100000000+CAST(cpu_ticks AS BIGINT)%CAST(100000000 AS BIGINT) as your @TimeNow