How to do a license to expiry on a date?

Hi,

Ok I have a number of assets that are displayed on mapping. We have to buy a license for displaying the assets on the mapping. I need to figure out a way that I can put some "license" with each asset to tell me when they expire but this "license" must be updateable by the end user.

So for example

Asset 1 - expires on 01/01/2011
Asset 2 - expires on 15/01/2011
Asset 3 - expires on 01/02/2011

My first thoughts were to use the ToFileTimeUtc function of the date/time. So 26/05/2010 15:39:11 gives me 129193619519710269. I am presuming that it's incremental so I can say if Field("License") < now.ToFileTimeUtc then license has expired.

I was also considering converting it to HEX and maybe reversing the hex string.

129193619519710269 = 1CAFCE996B8243D = D342B699ECFAC1 or maybe D342-B699EC-FAC1

I'm wondering if anyone has used something better?

Jim