Monostable multivibrator problem
This circuit relies on inverted edge RC delay from rail to mid voltage threshold for trigger  (R1C1=T1) 

That leading edge then uses that period to charge up C2 using the low dynamic resistance of D which I refer to as T2= ESR(D)*C2 &lt; R1C1.  We choose T1 and T2 so that T1 is bigger yet insignificant compared to the desired stretched output pulse of T3 when T1 has timed out and D is no longer conducting leaving the decay time of T3=R2*C2.

Edge triggered 1-shot (monostable)

T3>>T1>>T2  means the output pulse width of 1 shot comes from the decay of R2C2 but the edge trigger detector R1C1 is long enough to charge up C2 with ESR(D)

This is easily satisfied since C2 is shared by D to charge and R2 to discharge and the ESR of all diodes is roughly 0.5 to 1/Pd [Ω] and most circuit boards are reliable to use with xx MΩ so  very wide range of pulse widths is possible with CMOS using analog RC delays before we need to consider binary counters.