Macro changing all previous cells not just the one I want

So I run a small transport company and created a spreadsheet to track departure times.

Have written the macro as below

Sub T11X()
'
' T11X Macro
'

'
Range("A18:H18").Select
With Selection.Interior
.Pattern = xlSolid
.PatternColorIndex = xlAutomatic
.ThemeColor = xlThemeColorDark1
.TintAndShade = -0.499984740745262
.PatternTintAndShade = 0
End With
Range("W18").Select
ActiveCell.FormulaR1C1 = "=now()"
Selection.NumberFormat = "h:mm"
End Sub

I have multiple macros with the same information but change the cells on each. the problem is that the button when clicked is changing the value of every previous entry

Not sure why, Cheers in advance for any help