When condition true copy past values only.

Dear all,

I have two column,(Time and Value),

Time and value is changing.

time change 15:23:49 , 15:23:51, 15:23:55, 15:23:56 ...................Like that
Value change 0.8545 , 0.8543, 0.8581, 0.8586..................like that

Time Value Set time Final Value

15:23:49 0.8543 15:29:30 - 15:30:30 ???????

Time & Value will change. If Set time between 15:29:30 and 15:30:30 Need to take final value from value column and copy values only.After copy final value It should be unchanged.

please help me.

please reply.