The following code takes many, many minutes to run on several hundred rows.  
Does anyone have any suggestions that might speed it up?

Thanks in advance!

Option Explicit

Sub tester()
Dim i As Long
Dim area As String
Dim c As Range
Const sked = "0:30"

Application.ScreenUpdating = False

For i = 3 To Cells(Rows.Count, "C").End(xlUp).Row Step 1
 
If Cells(i, 1).Value <> "CT" Then
 
  area = Cells(i, "D").Value
   
Select Case area
  Case "CR1"
     For Each c In Range(Cells(i, "u"), Cells(i, "bg"))
           If c.Text Like sked Then
           c.Value = "CR1"
           Else
           c.Value = "X"
           End If
     Next c

  Case "CR2", "CR3"
     If Cells(i, "E").Value Like "*CR1*" Then
           For Each c In Range(Cells(i, "u"), Cells(i, "bg"))
           If c.Text Like sked Then
           c.Value = "OTH"
           Else
           c.Value = "X"
          End If
     Next c
    Else
     Range(Cells(i, "u"), Cells(i, "bg")).Value = "X"
     End If
 Case Else
     Cells(i, "U").Value = "X"
   
End Select

Else
Range(Cells(i, "u"), Cells(i, "BG")).Value = "X"
 ' GO TO NEXT
 
End If
 
Next i
End Sub