complex IF condition

Hi
I have a clock running on the background with hours and minuts and i have columns that each column is for a specific time - 10:45, 11:00, 11:45...etc
each one of the columns has about 10 rows for each stock quote.
i want each cell to check if the time at the head of the column is the time at the running quote then to take a the number from another cell and if its not than not to do anything.
in each cell currently i have this formula: =IF(AND(LEFT(P$7,2)=$C$2,RIGHT(P$7,2)=$B$2),$C13,0)
its basically checking the time for the column with the current time and put the value of C13 for this case in the cell. the PROBLEM is that one the time elapsed, it becomes 0 and does not save the value from before.
how do I get over this???

thanks
Danny