Breaker Tripping Mystery
That main breaker appears to be an RCD (Residual Current Device, also known as a GFCI or Ground Fault Circuit Interrupter).

So, apparently you have a ground fault somewhere in one or both of the circuits that are tripping the RCD. Since those circuits are both outside, they might travel through a common junction box or conduit that's suffered from water intrusion (and perhaps the nighttime temperatures lead to condensation that trips the breaker).

Some electrical equipment can lead to nuisance tripping of RCD/GFCI devices (such as electrical motors or fluorescent lights), though since you say that the breaker trips even when the circuits are not in use, this is likely not the problem.

I'd trace out the wires that lead out to those outside outlets and perimeter lights and see if you can find any damage or water problems.

There are a number of stack exchange questions on gfci tripping, which might help you isolate the problem.

If you can't find the problem, I'd call out an electrician to evaluate the circuits and if he can't find the problem, maybe try switching out the main breaker to see if that main RCD is faulty.

Providing your location would be useful, you're apparently not in the USA since that breaker does not seem to be common here.