it depends really, plants can muck up the cycle readings a bit because they take up ammonia, if they're taking up enough you may think that the filter is cycling when it isn't however this will only have a tangible effect with a lot of plants (around two thirds of the substrate planted as a rough guide). If you've got loads and loads of plants then it's actually a different process called silent cycling, I won't confuse you with details but if you're planning on very heavy planting then just ask and we'll give some more details so you can make an objective choice.
If you're just wanting a handful of plants then you can put them in, it's unlikely to affect anything either way