This closes #1030, fix date rounding error

date.go

@@ -20,6 +20,7 @@ const (
 	nanosInADay    = float64((24 * time.Hour) / time.Nanosecond)
 	dayNanoseconds = 24 * time.Hour
 	maxDuration    = 290 * 364 * dayNanoseconds
+	roundEpsilon   = 1e-9
 )
 
 var (
@@ -151,14 +152,14 @@ func timeFromExcelTime(excelTime float64, date1904 bool) time.Time {
 		}
 		return date
 	}
-	var floatPart = excelTime - float64(wholeDaysPart)
+	var floatPart = excelTime - float64(wholeDaysPart) + roundEpsilon
 	if date1904 {
 		date = excel1904Epoc
 	} else {
 		date = excel1900Epoc
 	}
 	durationPart := time.Duration(nanosInADay * floatPart)
-	return date.AddDate(0, 0, wholeDaysPart).Add(durationPart)
+	return date.AddDate(0, 0, wholeDaysPart).Add(durationPart).Truncate(time.Second)
 }
 
 // ExcelDateToTime converts a float-based excel date representation to a time.Time.

date_test.go

@@ -33,6 +33,7 @@ var excelTimeInputList = []dateTest{
 	{60.0, time.Date(1900, 2, 28, 0, 0, 0, 0, time.UTC)},
 	{61.0, time.Date(1900, 3, 1, 0, 0, 0, 0, time.UTC)},
 	{41275.0, time.Date(2013, 1, 1, 0, 0, 0, 0, time.UTC)},
+	{44450.3333333333, time.Date(2021, time.September, 11, 8, 0, 0, 0, time.UTC)},
 	{401769.0, time.Date(3000, 1, 1, 0, 0, 0, 0, time.UTC)},
 }
 
@@ -66,6 +67,19 @@ func TestTimeFromExcelTime(t *testing.T) {
 			assert.Equal(t, test.GoValue, timeFromExcelTime(test.ExcelValue, false))
 		})
 	}
+	for hour := 0; hour < 24; hour++ {
+		for min := 0; min < 60; min++ {
+			for sec := 0; sec < 60; sec++ {
+				date := time.Date(2021, time.December, 30, hour, min, sec, 0, time.UTC)
+				excelTime, err := timeToExcelTime(date)
+				assert.NoError(t, err)
+				dateOut := timeFromExcelTime(excelTime, false)
+				assert.EqualValues(t, hour, dateOut.Hour())
+				assert.EqualValues(t, min, dateOut.Minute())
+				assert.EqualValues(t, sec, dateOut.Second())
+			}
+		}
+	}
 }
 
 func TestTimeFromExcelTime_1904(t *testing.T) {