Timers are small devices with some wheel and push button – they do turn on or turn off lights in the tank. They are important! Better if lights are always on then shut down!
There are three timers: two on the left and one on the right. First on left, closer one, shuts down or turns on the main two white light tubes on the back of tank. The other one does the blue round lights in the middle of tank.
One on the right is for blue/pink tubes closer to you.
The second blue light that is closest to you is in the black tube on the top of the glass below the lid and it is combined with white light and these ones are not on timer! I always keep the blue on and switch manually every night and morning the white light only. It is better to keep the blue on!
If you forget the white – it is ok, but try to turn it off in the evening and turn on in the morning.