How to make my automatic night light circuit dimming?
Figure 1. Variable duty-cycle from 555. Source: Electronics Tutorials.
You should be able to make the circuit do what you want with the addition of a pair of diodes - one to provide a path to charge C1 and one to discharge. By adding a resistor - your LDR - into one or other path you can vary the ratio of on to off time. Provided the base frequency is high enough the flicker will not be visible to the eye.
Form the linked article:

The charging time of t1 = 0.693(R1 + R2)C is modified to take account of this new charging circuit and is given as: 0.693(R1 x C). The duty cycle is therefore given as D = R1/(R1 + R2). Then to generate a duty cycle of less than 50%, resistor R1 needs to be less than resistor R2.

Measure the resistance of your LDR in dark and light conditions and plug the values into one of the many online 555 duty-cycle calculators.