If your filter is properly matured already then you could stock fish straight away, but putting a new filter on a old tank for a while doesn't guarantee this (but it will help the filter mature more quickly and was a good move).
The other thing is that leaving fish out of the tank for as long as possible means you can turn the CO2 right up above 30ppm and get your plants nice and established before any fish go in. Fish produce ammonia and this is why we need a mature filter, but ammonia is also an excellent trigger of algae! By leaving the fish out for a few weeks you let the plants get going and reduce the chance of getting algae.
I would at leaving it fishless for at least 2 weeks then, if you don't get any nitrite readings after that, stock some algae eaters only. After a few more weeks without any problems you can then start adding your shoaling fish. I know this seems a long while to wait but you plants will thank you for it and your tank will look much better with lush plant growth.