's 22yards' link again as you say doesn't work for you. This one
is another one, though the light will turn on only once in the predefined time range. Perhaps you want to mix different types?
I found it googling with "zeitschaltuhr zufallsgenerator". "zeitschaltuhr random timer" works well, too.
I'm sure you can find them on the big online electronic retailers as well, including brack.ch, amazon.de, digitec.ch (though many complain about customer their service), conrad.ch, etc. What will be common is that they're electronic, as opposed to mechanic.