tracking flow / lead time need help

Hello
What I'm trying to do is create a worksheet to track and improve flow time.
So in cell 1A i need to be able to scan in a product (0001234123), in A2 have it input current time and date. Then up to 7 days later I wan to be able to scan the same product code (0001234123) have it find where it was first scanned and add the new current date and time in A3. finally in A4 show the total time between the two scan's. I will be adding hundred's of different product numbers to it a day and want to be able to track the start and finish times on all of them.

Thank you for you help
Dave

I looked at them. Thank you for your help. The issue I'm having is I want to make it a simple to use as possible. There will be 3 shifts for people using it. I was hoping to have a computer using a shared file at the start and one at the end. All the operators would do is scan the bar code on the product. one point would start the clock/log in the part number the other would stop the clock using the bar code scanned to find the first time it was scanned and add a finished time in the cell next to the start time. I'm not sure if I'm being clear or not. If you don't understand please let me know Ill try to explain it better.
Thank you again for you help.

Dave