Alex,
From your description, it’s a very basic contactor circuit. One, which probably can easily be found if searched for on google or in a basic training manual. There are assumptions made here due to lack of information:
The contactor coil pins, A1 & A2 are connected to the timer, so when the N/O timer contact closes at the required time, the contactor coil will be energised. The two N/O contactor contacts (pins 1&2 and 3&4) will both close when the coil is energised. Therefore live (pin 1) will supply pin 2, so supplying live to the lights. Neutral (pin 3) will close the circuit with pin 4.
Edit:Typing '2 pole contactor circuit' into google revealed plenty of examples...sorry but its really not hard.
I would suggest going to Maplins and buying some 12V DC relays and play with these using a power supply and some lamps. Won’t cost much but will be educational, safer than playing with mains.