You can add them almost immediately. The ammonia during the cycle will not hurt the plants. In fact, when I was cycling my second tank (I too contracted MTS
), one of the most knowledgeable forum members on here referred to it as "yellow gold" for my plants. And I must say, he is right. The plants that are in the tank are growing like crazy, despite the high ammonia readings.
Middlechild makes some valid points, but I think there are some very low maintenance plants you could start off with as a newbie. Just do your homework - although regular aquarium gravel will suffice for growing aquatic plants, there are some much better alternatives out there that would give you a leg up from the get-go if you decide to go with live plants. He mentioned lighting too, and that is important. Most stock hoods come with lights that are barely sufficient (if even) to grow only the lowest light requiring plants.
Again, look around, read some of the threads on this forum (and the FW
planted forum), and check out some of the tanks people have started (most of the members have some photos of their tanks, lots of times they have links to them in their signature blocks like mine on the bottom here). The fact that you are here early means you will have a massive advantage over the people that just pick up a bunch of fish stuff and try to do this without any prior knowledge (like I did!)
Again, I have to caution you too - be leary of advice received at some of the larger chain type pet stores and even some smaller LFS
(local fish stores). Many times, their objective is to sell you as much as they can, or in some cases, they just don't know enough about the items they are selling. Ask here... someone has experienced what you are inquiring about, and can give you the no-money-involved truth.