How to insert Time in a range of excel sheet which should not update automatically?

Friends I want to insert time in a range which should not get updated automatically. For example if there is any value in cell no k5 then the current time should automatically be inserted in cell no N5. Similarly if there is any value in k6 then the current time should automatically be inserted in N6, so on.. One more thing I Wish to bring in your kind notice that there is also a formula in entire column K, so If I type any value in any cell left to column K for example- if there is any data in A5 or B5 it will show the calculated value in k5. similarly if there any value in any cell left to k6 then its calculated value will be shown in k6 and so on. I tried to use this formula-
=IF(K5<0,"",IF(K5=0,"",NOW()))
This formula is working but it is auto updating the time with the system's clock. I want it should not update the time. Moreover, i also know that ctrl+shift+; inserts the current time in the selected cell and it does not auto update the time also, but it is useless in the present scenario. You can see the snapshot also- http://i.imgur.com/3JIwORg.png PLEASE HELP ME...THANKS A LOT...

paste the code in the worksheet event (right click on sheet tab > view code)

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whenever any value updates in column K, current time will insert in col N