The solution I give does *not* create a final Timer element with a variable duration. Instead, the solution I suggest (which, in my opinion, is simpler and cleaner, at least when implemented in PCIbex) consists in starting a Timer element at the beginning of the trial of a fixed duration, ie. the intended overall duration of the trial, and wait for it to elapse at the end of the trial before proceeding to the next one
The excerpt you quote includes three timers with a variable duration: D1 (400ms–1600ms) RT (0ms–1700ms) and WAIT (3500ms minus D1 minus RT). Then there are two timers with a fixed duration: D2 (100ms) and D3 (400ms) which makes for a total of 500ms. Because of how WAIT is calculated, adding the duration of the five timers totals to 4000ms
I misunderstood your previous messages as suggesting that you meant to have a total trial duration of max(D1)+max(RT)+D2+D3, which is why I proposed creating a Timer element of 3800ms. But if you want to replicate the design from that quote, set the very first Timer element (the one you need to wait for at the end) to 4000 instead
Jeremy