Does anyone make timers (say for a porch light) that automatically
adjust the off-on times to adjust for changing sunset times as the
seasons progress?

alansea...

If such a timer exists, I'm unaware of it. Since the 
time of sunrise and sunset changes on a daily basis,
creating an offset in the timing mechanism which not
only accounts for this difference but also for the
twice-a-year transition into and out of Daylight
Savings Time would be relatively complicated.

The simplest solution for this is to use a photoelectric
controller to turn the lights off at dawn and on at 
dusk. An example of such a controller is this one from
LightingUniverse.com:
http://www.lightinguniverse.com/products/view.aspx?af=232&family=10573

This kind of controller responds to the presence or
absence of sunlight, switching the power accordingly.

Note that this unit will control up to 500 watts of 
lighting, which would allow you to control several
outdoor lights. You may be able to locate a less
expensive model, at Home Depot or your local lighting
specialty store, which would allow you to control
a smaller wattage, such as a single porch light.

Another option, if the product exists, might be a 
smaller photocell controller which screws directly
into the light bulb receptacle and allows a bulb
to then be screwed into it, such as is used for
indoor sound-activated controllers. I didn't find
this product online, and it may not exist, but if
it does, your local lighting specialty store or 
Home Depot should know about it.


I hope this brightens your day!

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sublime1-ga


Searches done, via Froogle:

"outdoor lighting" photoelectric control
http://froogle.google.com/froogle?q=%22outdoor+lighting%22+photoelectric+control

Although photocell controllers have largely replaced timers for
lighting control, as sublime1-ga says, some timer manufacturers do
still make timers whihc compensate for the changing seasons. The major
names include Venner and Sangamo, and you should look for models which
include a "solar dial" which tracks sunrise and sunset.

The Sangamo technical information says:

"and with the solar dial versions, ON/OFF switching which tracks
sunrise and sunset. The S250 & Q550 switches are controlled by an
electronic quartz module with both ensuring accurate time-keeping. The
Q550 module has a back-up battery providing a 100-hour reserve in the
event of a power failure. With the easily-read dial face marked in
15-minute divisions, these switches also offer high timing resolution,
permitting power to be switched on for periods as short as 15 minutes,
to an accuracy of ± 3 minutes."

The models 550 and 553 listed have a solar dial.
http://www.tlc-direct.co.uk/Main_Index/Timers_Index/Timers_Sangamo/index.html
There is a link from that page to Technical Information in PDF which
includes details of choosing and setting a solar dial. Because the
times of sunrise and sunset vary with latitude, you need a dial
corresponding to your geographical zone.

sangamo.co.uk also list the Suntracker range of products which they
say "The unique flexibility of the Suntracker Series means that the
products can be programmed to be used anywhere in the world. ... 
Automatic Summer / Winter changeover,  Timed Offset - in order to
cater for political time variations"

There is no need to compensate for summer time, as the sun itself
doesn't change the time at which it rises and sets; summer time is
purely for man's organisational (in)convenience.

The information listed above is for UK suppliers but Sangamo say:
Outside the UK, please contact by enquiries@sangamo.co.uk

For a residential porch light application I would agree with
sublime1-ga's recommendation for a photocell - it will be considerably
cheaper than one of these timers, which are designed for industrial
use. However, they do exist.

Owain