Anyone know an Excel formula to convert Excel Date/Time to a Time-stamp?

I could use the UNIX time code, but since that runs out of headroom in 32 bit code in 2038, I’d prefer to use a conversion using a 64 bit code. Any Visual Basic programmers that can give me a formula that will work in Excel 2007?

I have a bunch of product reviews. The reviews are on a remote review service site, and I can download a CSV file of them from there. I want to add Schema.org Rich Snippets about reviews, reviewer name, review date, star rating, etc. to help SEO for Google and Bing.

Many apply to the same product ID. But to store them in a database, I have to give each one its own unique object ID yet keep that object ID somehow related to the ID of the item reviewed. I want to come up with some scheme for sticking a unique suffix on the reviewed item ID, because no two lines in the spreadsheet can have duplicate object IDs.

If timestamping is out of the question, is there a formula that would find duplicate Reviewed-item IDs and build a unique Review ID using the Reviewed-item ID + a sequential number suffix, or a row-number or cell-number suffix?

I’m not concerned with the method. The ideas mentioned are just food for thought. If there is an easier way, I’m all ears. Whatever’s the simplest way to get unique Review IDs is what I’m looking for.