You need to wrap the numbers in quotes like shown in the following example
DateTime =
ADDCOLUMNS (
CROSSJOIN(
CALENDAR(DATE("2000","1","1"),DATE("2025","12","31")),
UNION (
ROW ( "Time", TIME ( "1", "0", "0" ) ),
ROW ( "Time", TIME ( "2", "0", "0" ) ),
ROW ( "Time", TIME ( "3", "0", "0" ) ),
ROW ( "Time", TIME ( "4", "0", "0" ) ),
ROW ( "Time", TIME ( "5", "0", "0" ) ),
ROW ( "Time", TIME ( "6", "0", "0" ) ),
ROW ( "Time", TIME ( "7", "0", "0" ) ),
ROW ( "Time", TIME ( "9", "0", "0" ) ),
ROW ( "Time", TIME ( "10", "0", "0" ) ),
ROW ( "Time", TIME ( "11", "0", "0" ) ),
ROW ( "Time", TIME ( "12", "0", "0" ) ),
ROW ( "Time", TIME ( "13", "0", "0" ) ),
ROW ( "Time", TIME ( "14", "0", "0" ) ),
ROW ( "Time", TIME ( "15", "0", "0" ) ),
ROW ( "Time", TIME ( "16", "0", "0" ) ),
ROW ( "Time", TIME ( "17", "0", "0" ) ),
ROW ( "Time", TIME ( "18", "0", "0" ) ),
ROW ( "Time", TIME ( "19", "0", "0" ) ),
ROW ( "Time", TIME ( "20", "0", "0" ) ),
ROW ( "Time", TIME ( "21", "0", "0" ) ),
ROW ( "Time", TIME ( "22", "0", "0" ) ),
ROW ( "Time", TIME ( "23", "0", "0" ) ),
ROW ( "Time", TIME ( "24", "0", "0" ) )
)
),
"DateTime", [Date] + [Time],
"Hour", HOUR ( [Time] )
)