I hope this has an easy answer.
I have an outdoor solar light set and it has one collector. it works fine, but takes hours after dark to come on. All the other solar lights in the yard are on, but not this one. When I get up in the middle of the night it is working fine (it's on), and stays on until daybreak. It runs for hours once it's on.

What in the devil could be causing the delay with switching on? it's truly dark outside...

 

The very cheap Light-Dependant-Resistor is sunburned and/or has rain-water or condensation damage. It has happened to many of my solar garden lights.
Some lights have severe rust (from the cheap on-off switch and cheap battery cell) all over the circuit board.