I have a macro for clock running in Excel. Data in one cell is constantly changing. At a specific time, I want that cell at that time be copied into another cell. The value in that cell is constantly changing. How do I do this?

For example, stock prices, they are constantly changing on my spreadsheet
and at 10:30 I want the price to be copied into a specific cell.

Thanks for your help in advanced!
Cynthia