In an established tank you have bacteria present on the glass, decorations, filter box, everywhere, so a new filter cartridge is not a problem - no need to seed it. I have even replaced entire filters with a brand new piece of hardware and media on an established tank with no trouble whatsoever.
If you are trying to set up a new tank and seed the filter media prior to starting it up, I like to put the new filter in an established tank for about 2 weeks beforehand. I do this with biowheels and sponge filters also. That's how long I "think" it takes for the bacteria to colonize.