The simplest solution I know of is to use a CMOS Schmitt Trigger such as the 74C14, 40106, etc.
Connect a capacitor from the input to gnd and a resistor from the same input to Vcc.
When the power is applied, the capacitor is discharged and starts charging.
When the capacitor voltage reaches the threshold voltage, the output of the Schmitt goes low.
The delay will be about one time constant. So for a 3 s delay, use say a 10M resistor and a 330 nF capacitor.
Len