As BUU said: use the flipflop operator. it takes the form of expression1 .. expression2 and evaluates as false until expression1 is met and then triggers to true until expression2 is met

So basically what BUU does is setting expression1 timestamp > threshhold so that it is met by your criteria and expression2 is 0 which equivalates to false. So that after expression1 is met for the first time the if statement continues to return true until the whole file is processed.

If you want to know more about the flip/flop operator (and why it's easy to confuse with the range operator i recommend GrandFathers excellent Flipin good, or a total flop?