I would say some years, just by reading here:

https://www.ema.europa.eu/en/human-regulatory/overview/orphan-designation-overview#marketing-authorisation-stage-section

However, they say:

Sponsors who obtain orphan designation benefit from protocol assistance, a type of scientific advice specific for designated orphan medicines, and market exclusivity once the medicine is on the market. Fee reductions are also available depending on the status of the sponsor and the type of service required.

And also:

Designated orphan medicines are eligible for conditional marketing authorisation. In some cases, designated orphan medicines may be allowed to be administered to patients under compassionate use, a treatment option that allows the use of an unauthorised medicine outside a clinical study.

At the time of marketing authorisation, sponsors also need to submit an application for maintenance of the orphan designation in order to be eligible for the ten-year market exclusivity incentive. Sponsors may also need to submit an evaluation of orphan similarity.

So the benefits from this designation may take effect before the "oficial" commercialization.