If the soil is pre-fertilized then you may be right for the first 4 or 5 nodes- but that's hard to guess when each brand will be different. Just give it some plain kelp extract (one wish no added fertilizer like fish emulsion) to condition the soil. That maxicrop has NPK in it, so it's a fertilizer not just a kelp extract. Seasol is one such example of a plain extract and is safe to use without fear of burning (since it's not a fertilizer).
Because you know you have some nutes in the soil but not sure how much, look at your leaves every day. The first signs of Nitrogen deficiency will appear in the oldest leaves down the bottom. If you get to the point that any pale is happening down there, hit them with a standard dose of the yates or maxi crop- but be aware they are both fertilizers so only use one of them. If they grow up looking a nice green and get to the 4 or so plus node size then you could consider starting out a light dose of fertilizer to keep things from getting deficient. I'd suggest doing it at only half or even a quarter of the strength that first time if it's all still looking green and then wait a week and start doing regular dosing from then on.
