Plot count of rows by hour, each date separately, from non-standard datetime values, in Google Sheets

Choose Insert > New sheet and enter this formula in cell A1:

=arrayformula( 
  query( 
    { 
      query( 
        if( 
          len(Input!A1:A), 
          { 
            text(datevalue(left(Input!A1:A, 10)), "yyyy-mm-dd"), 
            hour(timevalue(regexreplace(Input!A1:A, "(d+) (d+)$", "$1:$2"))) 
          }, 
          iferror(1/0) 
        ), 
        "select Col1, Col2, count(Col2) 
         where '" & text(B1, "yyyy-mm-dd") & "' <= Col1 
           and Col1 <= '" & text(B2, "yyyy-mm-dd") & "' 
         group by Col1, Col2 
         label count(Col2) '' ", 
        0 
      ); 
      { iferror(sequence(24)/0, "baseline"), sequence(24), iferror(sequence(24)/0, 0) } 
    }, 
    "select Col2, sum(Col3) 
     group by Col2 
     pivot Col1 
     label Col2 'Hour' ", 
    0 
  ) 
)

Then create a chart based on the result table.