JTrader,
You would need to do at least a little programming in order to do this. Basically you could create a sub routine that records the value and then calls Application.OnTime to have it callback at a given interval after you initially called it.
Sub record()
With Sheets("data")...
I agree with blah....neither method would yield a result that is significantly better by any major factor, so it makes the most sense to stick with whatever is simplest.
I actually just wrote a small article on my blog about taking in price update data and creating your own simple time series and indicators from it. Although I typically work in C#, but I don't see any reason the code wouldn't be somewhat similar...