Должно быть немного быстрее:
Dim v, rng As Range
For Each cell In irow
For i = 1 To arr_size
If start(i) > Var1 Then
v = cell.Value
If v > start(i) - arr1(i) Then
If v <= Var2 Then
If rng Is Nothing then
Set rng = cell
Else
Set rng = aplication.union(rng, cell)
End If
Exit For
End If
End If
End If
Next i
Next cell
If Not rng Is Nothing then rng.Interior.ColorIndex = 22