I did try using the offset with the same pattern as you did, but I couldn’t tell it was changing anything.
The clock always started with whatever I set the duration as.
My original requirements can be found here. https://community.xibo.org.uk/t/countdown-timer/7585
I’m hoping one day the Clock widget will have a timer option and allow you to set a future date and time and will automatically calculate the time that needs to be displayed on the timer.