Cycling planted tanks is was more flexible and varied a process than the simple fishless cycle. As eagle noted it depends on a variety of things. How many plants, what plants, how much light CO2 and ferts are involved?
The more plants that are involved and the faster growing they are the less the need for bacteria becomes. Plants come with bacteria on them as well.
There are several schools of thought on this issue. My preference is to set up and plant the tank and let it sit for a while to allow the plants to establish and then I test the tanks ability to process ammonia by adding ammonia to 2 or 3 ppm. How the tank handles this over the next 24 hours will give one a good idea of where the tanks stands. Bear in mind that the purpose in cycling tank is to make it safe from ammonia etc. for the fish and inverts. because plants consume ammonia, this means less bacteria will be needed. Some combination of the plants and bacteria will do the job. How much of each is not important, that the ammonia etc. is being handled is what matters.
Also how one is willing to stock the tank matters as well. In fishless cycling the ammonia dosing is higher than a tank will ultimately produce in order. to insure there will be more than enough bacteria. But it is also set at this level to also insure one can add a full fish load all at once. If one is willing to stock more gradually, then even less ammonia handling capacity is required to begin that stocking process. If you are willing to stock in several additions instead of all at once, your tank needs to be able to handle less ammonia to begin adding some fish. Under these conditions processing 1 ppm of ammonia in 24 hours would mean you could start the staged stocking.
As eagle noted, if you can also seed bacteria from established tank (and you are not planting heavily), the combination of plants and seeding will often get you cycled instantly, or almost cycled so that only days are needed not weeks. Again I find the easiest way to determine how "cycled" a new tanks with seeding and live plants might be is to dose ammonia and test. In these cases the most important concern if the ammonia drops to 0 in a day or two is to insure there is no nitrite. The plants will not convert ammonia to nitrite the way the bacteria do. So when the ammonia drops to zero fairly fast, all you need to insure is that no nitrite is being created and not handled by the bacteria yet.
One observation- plants consume nitrate. In well planted tanks it is typical that one will test 0 nitrate in a tank. Tanks with plants, but not a ton of them, will still tend to show lower nitrate levels even if they are not 0. This all means that testing for nitrate in a newly set up planted tank may not provide any useful information relative to cycling.
Lastly, in tanks with low levels of plants which grow slowly and will be in a low light tanks, it may just be easier to cycle the tank normally (with seeding if possible) and then planting after its cycled. When doing this I would suggest lowering the ammonia dosing levels from 3 ppm down to 2 ppm. The lower level of planting should still take up a fair amount of any slack when they go in.
