A search on Amazon, Lowe's and Home Depot web sites showed a small set of such timers, but one seemed particularly interesting. One problem of using a fixed time to turn the front lights on is that in the Winter it gets dark earlier, and in the Summer it gets dark later. The ST01 Timer from Intermatic includes an "Astro" feature that knows when dusk (and dawn) occur in your location and can be set to turn the light on at dusk. So we bought one of these ($34.55 at Home Depot).
First thing we do is remove the old switch
The other switch is for the light in the entrance way. We end up with two wires to control the front porch lights.
The ST01 Timer comes with a standard paper installation guide, but the documentation on this guide is terrible.
There is a "mode" button that controls what is happening. As you cycle thru the modes, there are modes that show up that the installation guide does not even mention. They say to open the battery drawer to install the battery, but it is not at all clear how to do that (until after you have opened the battery drawer).
But it's a light switch, so from an installation point of view, installation is pretty easy. Attach the black wire and blue wire to the two wires that go to the front porch lights. The red wire is not used. Attach the green wire to the ground wires. Done.
Bend the wires so that they all fold into the electrical box and use the two screws (top and bottom) to hold it in place.
Oops. Now we see that the new switch is one of the large rectangular switches, not the small toggle switch, like the one for the front entranceway. So the old switch plate won't fit. And if we get a new switch plate, we also need a new switch for the front entranceway. So back to Home Depot, to get a new switch ($1.98) and switch plate ($1.59) for the "Decora" style of light switch. Remove the old toggle switch and put in the new Decora switch for the front entranceway, then put on the new switch plate.
So that took longer than expected, because of the unplanned for trip to Home Depot for the new switch and switch plate, but things should work better now -- the front porch lights should come on at dusk and go off at 11:00 pm, when we go to bed. Even if I forget to turn them on. Or off.