How to SELECT all records where there is not another record with the same key within a given time offset?
maybe you can try something like :

select ds1.*
from SampleData ds1
left join SampleData ds2 on ds1.id = ds2.id 
    and ds1.timestamp &lt; ds2.timestamp
    and ds1.timestamp &gt; dateadd(hh, -5, ds2.timestamp)
where ds2.id is null