Using timers to disconnect certain loads at night?

I do it by running those items on a low voltage disconnect set rather high, like 12.7v.  That way discretionary items are automagically turned off when charging stops.

LVD --> relay --> opportunity circuit *

It was surprising to see how little power I use at night in my campervan with discretionary loads turned off that way.  

If you aren't using the LOAD output of your solar charge controller you can use the LVD on it to do this without buying any other gear.
This timerless approach has an additional benefit of not needing adjustment as the seasons or daylight savings change;  it takes its cue from the sun.



* ok, it's actually LVD --> delay --> relay --> opportunity circuit.  In my setup Vlvr == Vfloat;  adding a delay allows the charging system to
climb past Vfloat to Vabs in the morning before engaging the opportunity loads.

I have a load I WANT TO TURN OFF at first daylight. I use a relay connected directly to the solar panel.  Relays will typically close at nearly half their rated voltage and open at almost 20%.  To the relay I add a zener of about 1/3 the relays coil voltage in series.  I actually use a TL431 adjustable zener to set the exact voltage, but a zener will work well enough.  This is simple, cheap and would  also work for day loads.  Opportunity loads are best left to voltage sensing.  I use a micro and some loads don't turn on till 13.9V on the battery. The selection of pre-made boards is slim with a dropout in the 12.7 range and time delay which I consider a must. I haven't found any.

Note that if you want DC load control, many solar controllers (most Chinese ones, even some better ones like the Midnight Kid) do low-side control - the switching occurs in the negative rail. That presents a problem in any negative ground system like an RV because the battery and loads are all connected together with ground, so the controller's can't control loads. It makes the load control useless. Morningstar Prostars have high-side control and should be able to be set as desired - "after sunrise, on" and "after sunset, off". I'm sure there are others.