The timer has metal cogs that can be moved in towards the center of the wheel. There are numbers from 1 to 12 on the wheel. It moves clockwise. I have the correct time set on the other part of the timer. I just need to know how many cogs to push towards the center and what they mean. Is the first one how many days? Or the time you want the filter to go on? Thank you in advance. I hope I was clear.

You did not mention a model, but here are some mechanical timers from Intermatic:

Intermatic Timers - Mechanical Time Switches - 24 Hour

Timers ususlly work in one of two ways that I know of.
One is the use of ON and OFF trippers. The other way is to have cogs for say 1/2 hr intervals. The cogs may need to be in one position for ON and the other position for off. So you may need 4 cogs in a row in one position and the rest in the other.

What you might have is a 12 hour timer. Your basially setting the time when you want the filter to back flush and for how long to back flush.

If you say have 24 cogs and a 12 hr timer then each cog represents a 1/2 hour period. If you wanted the filter to backflush at 3:00 AM in the morning, you need to set 2 cogs in a row at that time.

So, I'm guessing.