It's a pity this whole electrification project is running so late. According the to the Department of Transport and Infrastructure website, the track upgrade was finished by the end of July, so it is only the signalling and electrification crews still working on the track. The Noarlunga-Oaklands section should have been finished within the first few months of the shutdown. The team would have had 24/7 access to this section of track, and partial access to the track from Oaklands to Adelaide while other teams were upgrading the track.
The best example of how to how to do a project is the Middleborough Road grade separation in Melbourne. The line was closed 1 January 2007 and reopened 28 January, with 2 new bridges, a rebuilt station, 1.5 km of new track that was up to 6m lower than the original, and with electrification and signalling re-installed. To achieve this required over a year of detailed planning, plus preparatory night works such as pile driving. The engineers were from VicRoads, and probably had more experience with large projects than those from the public transport entity.
What is the difference in South Australia ? Is there such a short time between when the government agrees to fund a project and when physical works are to commence ? There is then not the opportunity for detailed planning and preparatory works.
The next large project is grade separation of the Outer Harbour line at South Road and Bowden. If there is less pressure to start works early, hopefully there is more time for detailed planning so the shutdown period is shorter.
Track works were only completed like a week or two ago for the Noarlunga Line not by the end of July like DPTI were claiming. Drainage and vegetation crews also needed access to the rail corridor so that would've slowed the electrification crew down further.
But yes it could've gone faster with better planning and more people employed to carry out this entire project.