Doc originally notified the applications for the minimum 40-working-day period set out in the Conservation Act.
However, Southland conservator Barry Hanson said in a statement yesterday many parties wanted to become involved in the process.
"What we heard from the public was that, because of the sheer volume and complexity of information accompanying the applications, they need more time to understand the issues and draft their submissions," Mr Hanson said.
The deadline for submissions on the applications lodged by Milford Dart Ltd (MDL) to build a single-lane commercial coach tunnel linking public roads in the Routeburn and Hollyford Valleys will now be February 20, while the Riverstone Holdings monorail concession deadline will be March 19.
Doc has so far received 120 submissions on the MDL tunnel application and 11 submissions on the Riverstone monorail application. Parties who have already made submissions will be notified of the extension, which will allow them time to amend them.
Mr Hanson said Doc wanted to allow for submissions which would lead to an informed set of hearings and that it did not want to restrict the opportunity for parties to be properly heard.
Doc will hold public hearings to consider submissions before reaching its final decision. Dates and venues for hearings are not yet set and will not be confirmed until the department has a tally of the submissions and the number of submitters who wish to be heard and has determined the issues raised in submissions.
However, Doc was still working around the dates initially notified, with hearings for the tunnel due to start in mid-March and for the monorail in mid-April.