Two ways to slow the flashing: Larger resistance values or larger capacitance.

 

How would I slow the rate of flashing?

In the post #19 circuit you'd increase R1 and/or C1.

 

With the component values shown the pulse duration is about 1.5 sec and the pulse interval is about 90 secs.

I see a pulse interval of around 4 minutes.

ak

 

LTspice sees a pulse interval of 87 sec (apart from the initial cap charge time of 230 sec).