Section 1 of the Northern Ireland (Executive Formation and Exercise of Functions Act) 2018 (c. 28) (“the 2018 Act”) extends the period under section 16A of the Northern Ireland Act 1998 (c. 47) for Northern Ireland Ministers to be appointed following the Assembly election on 2nd March 2017 until 21st October 2019. Section 2(1) of the 2018 Act allows the Secretary of State, by regulations, to further extend that period until 13th January 2020.
Link: The Northern Ireland (Extension of Period for Executive Formation) (No. 2) Regulations 2019
Source: Legislation .gov.uk