Another solution for this question.
Community: Calculate the time difference between two features in a non-spatial dataset
Table columns definition in the InlineQuerier:
SQL query statement is:
select a.SiteName, a.SampleDateTime,
when b._count is null then null
else round((a._epochtime - b._epochtime)/3600.0, 1)
end as TimeSinceLast
from Source as a left outer join Source as b
on b.SiteName = a.SiteName and b._count = a._count - 1
btw, why there is not datetime type for setting input table columns in the InlineQuerier?
FME 2014 SP3 build 14389
Dale@Safe replied to my question. See his comment. Thanks, Dale!