What I have done to overcome this problem is to record a macro, select the cell first then start recording macro - write in " =now() " and format the cell so it looks how you want it. Copy the cell and then paste values - stop recording.
Now you can run this macro in any cell. If you keep a " Book of Macros " seperate with your macros stored here then when it is open you can run the macros in any workbook you are using.