VBA: Alter VBA script to find a range

Experts,

I have a script that will make changes to the entire sheet.  I am wanting to only have it apply the changes to only A5:AC30.

Can some help me modify my code?

Sub FormatChangerSurveillance()

Dim cell As Range

For Each cell In Sheets("NOC Agent Daily S").UsedRange
cell.Replace What:=":", Replacement:="."
cell.Replace What:="AM", Replacement:=" "
cell.Replace What:="PM", Replacement:=" "
Next

End Sub

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