NIFL have announced the following dates for the Premiership Promotion / Relegation Playoffs

First Leg
Friday 4 May 2018 (kick-off: 7.45pm) – to be played at ground of Championship club

Second Leg
Wednesday 9 May 2018 (kick-off: 7.45pm) – to be played at ground of Premiership club

Confirmed:
Championship: There will be no pre-playoff in the Bluefin Sport Championship between the second and third placed teams as Harland & Wolff Welders have not applied for a Championship licence to gain promotion to the Danske Bank Premiership.
Championship: Newry City will participate as the highest placed eligible club.

TBC:
Premiership: Carrick Rangers (11th) or Ballinamallard United (12th) – both sides level on points with one game left to play (on Saturday 28 April).

https://www.nifootballleague.com/danske-bank-premiership/news/item/ni-football-league-playoffs