In an article I posted a while back I showed different methods of creating Time dimension in Power BI and Tabular models. The Time dimension I explained was in Minutes. In this post I show you simple way to create Time dimension supporting Seconds. As this is a quick tip, I only show you how to get the Time and ID columns in the Time dimension. If you need to add time bands (time buckets) check this out for more details.
Time Dimension in Seconds Grain with Power Query (M):
Copy/paste the code below in Advanced Editor to generate Time dimension in Power Query:
let
Source = Table.FromList({1..86400}, Splitter.SplitByNothing()),
#"Renamed Columns" = Table.RenameColumns(Source,{{"Column1", "ID"}}),
#"Time Column Added" = Table.AddColumn(#"Renamed Columns", "Time", each Time.From(#datetime(1970,1,1,0,0,0)+#duration(0,0,0,[ID]))),
#"Changed Type" = Table.TransformColumnTypes(#"Time Column Added",{{"ID", Int64.Type}, {"Time", type time}})
in
#"Changed Type" 
Time Dimension in Seconds Grain with DAX:
Run the DAX expression below in a new calculated Table in Power BI or SSAS Tabular model:
Time in DAX = ADDCOLUMNS(
GENERATESERIES(1, 86400, 1)
, "Time", TIME(0, 0, 0) + [Value]/86400
)