Select The Cell Same Row Next Column

The first code is on the top of the module.

Code:
Private Const OPEN_TIME_COL = 3
Private Const CLOSE_TIME_COL = 4

Code:
RowNum = .Cells(.Rows.Count, CLOSE_TIME_COL).End(xlUp).Row + 1
.Cells(RowNum, CLOSE_TIME_COL).Value = Now

So according to the second code, it records the closing time(now), in the CLOSE_TIME_COL(Which is D)
in the next availabe cell, from the CLOSE_TIME_COL....

But here is the part i am trying to change

Code:
RowNum = .Cells(.Rows.Count, CLOSE_TIME_COL).End(xlUp).Row + 1

So that, what it should do is find the last cell used in column C, (OPEN_TIME_COL) and shift right.

if the last cell used in C is C1, CLOSE_TIME.Value should be in D1

for example somthing like this... but this code doesnt work

Code:
RowNum = .Cells(.Rows.Count, OPEN_TIME_COL).End(xlUp).column + 1