Adding always hot receptacle to a ceiling light that’s on timer
At some point, you need to split the power for the receptacle separate from the light. Where/how you can do that depends on whether you have:


Panel->Timer->Light
or
Panel->Light->Timer (a switch loop)


The first method is what I instinctively think of, but depending on the design of the how building and when/how the light was added, you may have the second - a switch loop. If you have a switch loop then you can split the power at the light and everything is easy. But if not, them there are two ways to get power for the receptacle:


At the current timer location. This is normally the best way, but it requires running a new cable from the timer junction box to the receptacle. That may be easy, or it may be quite difficult.
At the light. This is actually quite easy if the light is not on a timer. As @Mazura suggested, if you can replace the existing light fixture with one that has a photo sensor (sometimes called "dusk to dawn") then you can:


Split the power in the junction box that supplies the light. Depending on how the light is installed, you may be able to add a split (pigtail wires) in that box, or you may need to install a new box next to it. But either way, everything can be close together and you don't need to run a new cable through the wall.
Either in the same junction box or in one next to it, install the receptacle for the security camera. Normally I'm not a big fan of receptacles in hard-to-reach places like a porch ceiling, but in this case that is exactly what you want, so that the power cable to the camera is not easy to reach. (I've seen a porch security camera with a wire hanging down to a wall wart plugged into a standard-height receptacle.)



Another advantage of changing the light to a photo sensor is that you no longer have to worry about adjusting the timing over the course of the year.