Help with Pulse Generator Circuit

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http://forum.allaboutcircuits.com – Hello Everyone. I am hoping someone can help me with a circuit (see attached) I am working on. It generates a pulse of a set length when a button is pressed. I have it working ok, but I am having trouble adjusting the pulse length (see attached) to exactly what I want. Right now the fall time (A) is 400us, the length is 35ms, and the rise time to 75% full voltage is about 11ms. What I can't seem to figure out is how to reduce the fall time and rise time without reducing the length. I really would like to have a fall time of less than 5us and a rise time to 75% of about 4ms with the length stay (Embedded)