When the method presented in the article works, it means that when they build their thingy something from the future must be there instantly (because of their full knowledge of the possibility of travelling to this 'portal'). Anything from any time in the future can travel to there.
First of all it will give some very strange implications. You can for example duplicate things very easily by sending them back in time, so it's not only a way to travel through time, but also a material-duplicator. Next there can exist things that have never been created or which are being created at the moment (draw a nice painting, go back in time with the painting and see yourself drawing the painting you're currently holding). In this way it would also be really easy to overcrowd the world. Thereby there would also be added more mass to the universe (there is a fixed amount of molecules in the universe, but when you duplicate something this way, the same molecules will exist twice).
I don't belive that there is a way to go back in time, but what IS possible is travelling forward in time, but there is no way of going back then. The only thing you need is an object that can move extremely fast (> 100000 metres per second for travelling forward a little, so you can travel a day forward in a decent time, but at least 250000 metres per second for making bigger leaps). It may even be possible to slow down time, but that is way more complex.
Self-confident people can create a machine to travel forward and send themself to the future to check out if the project succeeded and then go back to the portal. I can imagine the people sitting at the portal, waiting to get their "visitors from the future".