DC/DC step down timer
R3 will be in parallel to R1 after a certain delay which is fixed by R6 and C6.
Diode D6 will discharge C6 to the load ad power-off.
At power-up C6 will be a short circuit and will keep Q2 off.
At power-up R4 will keep Q1 off.
In the picture, R1 and R2 have dummy values.

To complete the design one has to set the values of:  R1,R2, R3, R6, C6