Here is an idea that manipulates the switching threshold point, by the D-type flip-flop, to terminate the timing cycle early. D1 is used as a low reverse-leakage diode with 2.2 V forward drop.
Circuit simulated in Proteus.
Normal triggered output duration.
Triggered output terminated by next trigger pulse.
Output can be turned on or off with alternating trigger inputs. While the output is in the on state, it will time out after the normal timing period set, if no more triggers gets applied.
Slower sweep.
