The A-League will become the first top-tier football competition in the world to implement video referees when Melbourne City host Adelaide United on April 7 with referee assistants able to influence on-field decisions with visual replays. Football Federation Australia says the length of time for decisions to be made is one of the concerns as it finalises the training for up to nine Video Assistant Referees.

For the most part during training and trials, correcting simple errors can take half a minute but at small stadiums and low-profile games with far fewer camera angles, that has proven more time consuming. The greatest concerns over the flow of play are incidents where on-field referees choose to personally review the footage on screens located at the halfway mark on the sideline.

During practice, it's taken nearly two-and-a-half minutes for a referee reviewing a penalty to run from the box to the halfway line to personally review footage of incidents that VARs cannot provide a definitive ruling on.

The FFA's director of referees, Ben Wilson, says the majority of decisions should be made efficiently and quickly however they are prepared to take their time in order to make the correct ruling, even if it slows the pace of the game.

"The main objective is to get the decision right, so that's the first priority. If that takes a little bit longer then that's OK." Wilson said. "There's no time limit as such but the expectation is that all of our decisions will be made within 30 and 40 seconds."

VARs have operated offline at 10 A-League games thus far and once they come into effect on April 7, they will only be involved in correcting clear errors, assisting with red cards, penalty decisions, offside calls and cases of clear mistaken identity. On average, they have only had to intervene twice per game throughout the offline trials. They will operate as assistants to the match referee and will not be able to overrule decisions, only to inform the man in the middle of any errors.

They will not intervene on contentious decisions, leaving it up to the referee to make brave decisions that are not clear-cut.

"We just want to correct clear errors. If there's a decision that's not contentious because it's so clearly wrong, they're the ones we want to fix," Wilson said. "The video referees are there for minimum interference and only there to be involved when there's going to be maximum benefit to football by overturning a clear error."