The idea is that that a biological filter builds up "good bacteria" These bacteria convert the fish waste from "nasty stuff" to "nice stuff"
(Or you could say that bacteria eat fish waste. The other analogy would be: Imagine if I left you in a warm swimming pool for a month, gave you food and a toilet, then after a week I take the toilet away.)
The bacteria occur naturally, and given some where nice to live (the filter media) they multiply over time. The more bacteria there are the more fish waste they can convert.
The bacteria also need oxygen as well as food, both are brought to them by the moving water. (From the pump)
If you switch the pump off (timer in your case) the good bacteria die. (no food or oxygen = starvation) Then when the pump comes on, it dumps a load of dead bacteria into the water, which is not good.
Its true that as soon as you switch the pump off all the bacteria do not instantly die, but give them a few hours and most will be dead.
While there are few "working" bacteria the fish waste contamination goes up, eventually the fish die.
In winter almost everything slows down, the only real constant is bacteria still die quickly.
The way round it is to keep the biological filter running 24/7 The fact you have an all in one makes no difference (apart from its efficiency) bacteria still need food and oxygen to live.
Good quality costs. Bear this in mind before you start.
Sorry if my reply is NOT want you want to hear, but what I have said is true.
We can only go by what you type.
A "thank you" costs nothing, but goes a long way.