A suspended Nauru opposition MP Roland Kun says processing 600 asylum-seeker applications in one week is logistically impossible.
On Monday, Nauru's government announced it would finalise the remaining 600 refugee claims at the Australian-run detention facility.
Mr Kun questions the quality of that processing, given each application requires extensive research work.
"I think they're just stating an intention but not being realistic as to what they can actually achieve in terms of time frames necessary to process applications."
Mr Kun says he is concerned about those asylum seekers whose applications for refugee status are rejected.
Earlier Nauru announced it was turning the facility into a so-called open centre 24 hours a day, allowing asylum-seekers freedom of movement on the island.
High court challenge to offshore detention begins today
Nauru's new open camp arrangement will be one of the issues brought before the court in a major test case beginning today in Australia.
The full bench of the High Court will sit today and tomorrow to hear a challenge to the lawfulness of the Australian Government's role in offshore detention.
The case is being run on behalf of a woman from Bangladesh who faces imminent return to Nauru with her baby after a problematic pregnancy.
It is the the lead case linked to a series of challenges being run on behalf of more than 200 people in similar situations who have been brought to Australia from Nauru and Manus.
They include men subjected to serious violence on Manus, women who've been sexually assaulted on Nauru and over 50 children, including 23 babies.
