An ACT Supreme Court judge found it could not be established beyond reasonable doubt that the positive alcohol test had been conducted with the two hour time limit.

Gregory Fletcher, 22, was hurt after his motorcycle was "clipped" by a car at a roundabout about 3.15am in June 2014, as he rode home from a friend's house.

He had not been drinking.

After the accident, he pushed his damaged bike home, woke his mother to assist with his wounds, and then consumed between 10 to 12 standard drinks.

After an hour, his mother became concerned about the injuries and convinced him to go to hospital.

The Emergency Department recorded his admission time as 4.49am.

A nurse then took blood at 6.48am, to test whether he had used alcohol or drugs, as he had been involved in a motor vehicle accident.

Tests must be conducted within two hours of presentation at hospital, after that time period the person can no longer be defined as a driver involved in an accident.

The nurse's notes recorded that she conducted the test one minute before the two hour limit expired.

But the recorded time of the test was taken from a different clock as that used to note the admission time.

The nurse, in evidence, could not say whether the time on the computer system and had been synchronised with the wall clocks from which she logged the time.

Analysis returned a blood alcohol reading of 0.135.

Mr Fletcher lost his job as an apprentice plumber when police immediately suspended his licence for drunk driving.

He fought the charge but was convicted by Magistrate Robert Cook after a hearing in July.

Mr Fletcher's lawyers, Ben Aulich and Associates, appealed the decision to the ACT Supreme Court and the matter was heard in October.

Acting Justice David Robinson, in a decision published last week, allowed the appeal and set aside the conviction.

Acting Justice Robinson said Magistrate Cook had erred in presuming the two clocks had been synchronised and that the blood had been taken within the last permitted minute.

"To my mind this fact could not be found to be proved beyond reasonable doubt unless there was evidence of the synchronisation of the two instruments," Acting Justice Robinson said.

"In my view where only the doing of the required procedure was done in the last minute, as judged by two presumptions from two 'clocks', a reasonable doubt is thrown up where there is no evidence that the two clocks have been synchronised.

"I have come to the conclusion that the tribunal of fact ought to have experienced a real doubt as to whether the prosecutor had made out his case to the requisite standard."

The judge ordered the conviction be set aside and dismissed the charges.