backdating employment allowance

If a sole director company employs someone towards the end of the tax year, which then makes them eligible for the employment allowance, is that allowance applied to the whole tax year? i.e. does the company get a rebate for the employer NIC paid on the director's salary from the start of the tax year, or does the employment allowance only kick in from the date that the new employee joins?

Hi Rebecca Webster,
If both a director and a new employee earn above the secondary threshold, the business can reclaim Employers NIC up to £5000 for the financial year. 
This applies to the entire year's salary of the director, not just the second employee who met the eligibility later.
For more details, see Employment Allowance: What you'll get.
Thank you.