It's good news, but health authorities have warned the number could be lower because of changes to the way cases are reported in the ACT.

The daily case update will now only include positive results reported up to 8pm the night before, which gives contact tracers more time to work out whether the cases were active in the community or not.

Chief health officer Dr Kerryn Coleman said it would give ACT Health more time to see where chains of transmission were continuing.

"Any cases that come in after 8pm overnight will be included tomorrow's case numbers. This is just a realignment. We will not be hiding or not reporting cases," Dr Coleman said on Saturday.

"But it does mean that today's case number is probably a little artificially low and tomorrow will be back up to possibly what we were seeing yesterday or the day before."

The ACT reported 16 new cases on Thursday and 12 new cases on Friday.

In previous days, the reporting cut-off has been 9am, which means cases are reported at the 11.45am press conference before contact tracers have determined their movements.

In the early part of the lockdown, every case had been active in the community during their infectious period. But more than a week after restrictions were imposed, some cases will have been quarantined throughout their infectious period.

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ACT Health Minister Rachel Stephen-Smith issued a word of caution about Saturday's lower case numbers.

"This is one day and it is likely we will see new cases over the next couple of days that had some period where they were infectious in the community," Ms Stephen-Smith said.

"But this is a really great sign that this is the lockdown working and this is contact tracing work and this is isolation and quarantine working."

And what would it take for the ACT to end its lockdown early?

Chief Minister Andrew Barr said the ACT would need solid a run of days where zero new cases were reported, beyond the 14-day incubation period.

"In order to come out of lockdown early, we would require day after day of zero cases and people not infectious in the community. The clear point is that coming out early, whilst there is still risk of virus transmission, could see the whole thing start again," Mr Barr said.

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