Also if I attempt to simulate this it does nothing. LED never lights and never see any output from IC1

Must be something wrong with the simulator as the circuit works fine on my breadboard.

 

Aren't TRI and THR supposed to be isolated in a one shot? TRI on VCC and DIS and THR together instead?

Not necessarily, that's what makes the 555 so versatile.
When first powered up with the switch open the LED is ON because the TRI input is low. When the switch is pressed C6 charges rapidly through D1 and R7 until it reaches the 2/3Vcc of the THR input. The output goes low and the DIS pin clamps the voltage at the anode of D1 at appx .02 volts reverse biasing D1 so C6 must discharge to 1/3Vcc before the cycle can repeat.

 

Not necessarily, that's what makes the 555 so versatile.
When first powered up with the switch open the LED is ON because the TRI input is low. When the switch is pressed C6 charges rapidly through D1 and R7 until it reaches the 2/3Vcc of the THR input. The output goes low and the DIS pin clamps the voltage at the anode of D1 at appx .02 volts reverse biasing D1 so C6 must discharge to 1/3Vcc before the cycle can repeat.

Thank you for all your effort in providing solutions and explaining. Something must be wrong with my simulator. I will build it on the breadboard and see what happens.

Is that a particular kind of diode you are using? The squiggly line is usually a Zener or a Schottky right?

 

The squiggly line is usually a Zener or a Schottky right?

It's a schottky but a 1N4148 should work as well.

 

I've read that I can build a voltage divider circuit to precharge the A2 capacitor to 1/3 VCC so that it is precharged before the first firing attempt.

Below is the LTspice simulation of a 555 gated astable circuit where the first period is essentially the same as the following cycles:

Schottky diode D1, R4, and pot U3 maintain the minimum Trig voltage on the C2 timing capacitor close to 1/3 Vcc.
Edit: I added a pot, similar to that shown by sghioto in post #20, to allow for component tolerances.

OR gate U2 keeps the input Enable signal from truncating the last pulse (if that's important) when it goes low.

 

Here's another version of the 5 sec delay timer. Holding the switch down does not restart the delay but will send a pulse every 5 seconds.
View attachment 283551

It's very odd, when I build this in MultiSim. It gives me a convergence error and then when I resolve the error it says it can't find it. Then when I run it it just outputs high forever. The LED stays lit perpetually and IC1 just outputs high forever.

You can confirm that this worked for you on the breadboard as shown in this diagram?

 

You can confirm that this worked for you on the breadboard as shown in this diagram?

Yes sir 100% and all the other circuits I posted.
Can you post your layout of the circuit in MultiSim?

 

I ran the circuit through MultiSim with the switch open and closed and it was spot on.

 

Yes sir 100% and all the other circuits I posted.
Can you post your layout of the circuit in MultiSim?

here is the complete sim, I will try what you did. You have no 10nf control cap?

 

You have no 10nf control cap?

It's optional also D2 can be a 1N4148 ,1N4149 or a BAT85 schottky.
R6 should be set at 46%.