I too grew very frustrated with the photo sensors and mechanical timers that typically control outdoor landscape lighting.
@binderth pointed you in the exact direction of what I choose to move forward with and has been rock solid ever since I deployed it.
I changed the electrical outlets where my landscape lighting transformers are plugged into AC power to Zwave outlets - this is the model that I used but any will do:
Once the outlets were included into my Z-Wave network I removed the analog timers and photo cells and created the following rules.
The rule utilizes the ASTRO BINDING to get SUNSET and SUNRISE times which I use to turn the lights on and off.
rule "turn landscape lighting on"
Channel 'astro:sun:home:set#event' triggered START
rule "turn landscape lighting off"
Channel 'astro:sun:home:rise#event' triggered START
I also have used an alternate version of this rule utilizing CRON to turn the lights on and off at specific times rather than at SUNSET and SUNRISE.
Let me know if you have any questions.