The legislative provisions for the Help to Buy incentive are set out in section 477C of the Taxes Consolidation Act 1997 (TCA), as inserted by section 9 of the Finance Act 2016. The incentive applies for the period from 19 July 2016 to 31 December 2019.
I can confirm that a qualifying refund under Help to Buy is paid in one lump sum by Revenue. A first-time buyer or self-builder will need to apply and claim online on http://www.revenue.ie/en/tax/it/reliefs/htb/index.html. Claims are verified by either the purchaser's builder ("qualifying contractor") or their solicitor in the case of a self build, and once verified, the refund is paid.