A day on the roof, but that is not the whole timeline. Here is what happens either side of it.
The install itself is the short part. Most domestic systems we fit are done in a single day. What people underestimate is the sequence around it.
Survey. Before anything is ordered, someone needs to see the roof: its structure, its condition, the loft space, where the consumer unit is and what route the cabling can take. A satellite estimate is good enough to decide whether solar is worth considering. It is not good enough to order equipment against.
Design and quote. Panel count and layout, inverter sizing, whether a battery earns its place, and what the grant reduces it to. This is where a year of bills is more useful than anything else you can give us.
Grant application. The SEAI domestic grant is applied for before the work starts, and we complete the application on your behalf. It is paid to you after the system is commissioned, not deducted up front, so budget for the full amount and treat the grant as a rebate.
Installation. Usually one day. Scaffolding where the roof needs it, mounting rails, panels, inverter, and the electrical work back to the consumer unit.
Commissioning and paperwork. The system is tested and certified, and the connection is notified to ESB Networks so you can be paid for what you export. Until that is done you are generating but not exporting.
Realistically, from first conversation to a working system, think in weeks rather than days, with the bulk of that being survey, design and grant rather than anything happening on your roof.