The candles I am using are achievement based and therefore each one has a different amount of time.
I have resorted to:-
a) Running a continuous bar count on each bar open = (Current Bar Number)
b) Recording the current bar number when a new trade is placed = (Trade Start Bar Number)
c) Calculating the number of bars between now & when the trade started = (Current Bar Number) - (Trade Start Bar Number)
A little crude and simple but appears to be working.
Many thanks for the input.