Probably setting a public deadline was a mistake to begin with.
In any case they were officially aiming to finish the report in 7-8 months vs. the 12 month ICAO target date:
(official NTSC statement in Indonesian -- NTSC to accelerate QZ8501 final report)
Kementerian Perhubungan Republik Indonesia - KNKT Mempercepat Laporan Akhir Investigasi AirAsia QZ8501
In April, Indonesia's Transport Minister Ignasius Jonan said that he expected the investigation to wrap up in June, ready for a ministry briefing in July:
(interview with Ignasius Jonan in Indonesian -- New route license for AirAsia withheld until QZ8501 final report completed)
Investigasi Pesawat AirAsia QZ8501 Belum Tuntas, Izin Rute Surabaya-Singapura Tak Jelas | IndoBerita.com