There are three different methods to activate and deactivate landscape lighting, timer plus a photocell, sequencer, and astronomical timers.
Timers and photocells have been around a while and have an advantage in their simplicity. The timer is set for an on and off time, the photocell overriding the timer when it senses light. This setup is usually easy for the anyone who has used a regular timer to understand and adjust. The downside is, photocells are delicate in nature and can be easily broken. Another downside is most timers do not have battery operated backups, causing many homeowners to believe the system has malfunction when in fact the timer is no longer set properly. Sometimes photocells in Minnesota can have problems with blowing snow obstructing the lens. This causes the lights to go on earlier than they should and waste electricity lighting up an already bright outdoors.
Photocells can vary in sensitivity and if two transformers are used at one residence they might never detect dusk at precisely the same time. In this situation a sequencer can be used to control both transformers. The sequencer at a secondary transformer takes input from the primary timer/photocell to go on and off at precisely the same time as the first transformer. This solution works well when transformers are in close physical proximity to each other. Transformers are often placed in different locations because of lack of access or the impracticality of running all the lights from one location. Sometime a remote trigger such as X-10 or other wireless devices are used to give control over multiple transformers.
A much more inexpensive solution than a X-10 module is an astronomical timer. Astronomical timers work by having the sunrise and sunset times for all locations programmed in the timer. There is no light sensitive part on the timer and the can have finer adjustments made to start times and end times with dozens of different programmed events. Astronomical timers have the major advantage of being more exact than photocell/timer combos. Astronomical timers have a batter back up so if a power outage occurs the device still functions properly. Outdoor timers can also have two a drawback is more technologically challenged individuals will have a harder time adjusting the timer.
There are always unique situations but generally astronomical timers provide the best value and the least hassle for homeowners.