An employee might be granted more than 90 days to raise a grievance if the employer has not given the employee a written employment agreement which explains the 90 days limit.
An employee must raise the grievance properly. This means the employee must explain to the employer what their grievance is (i.e. the facts that give rise to it), that it is a grievance and what remedies the employee seeks (e.g. lost wages and compensation for hurt feelings). Otherwise, the Employment Relations Authority won't hear the claim.
Even where an employer has genuine grounds for making a position redundant, and where the employer has carried out a proper consultation process, this may not be enough. The employer must also take care to allow the employee to depart with dignity.