As it is pot grown, you can easily leave the plant in its pot for a few days/weeks before planting it. Just ensure you keep the plant well-watered, and it gets enough sun. Don't leave it for too long, however, as you don't want the roots becoming root bound.
The Rowan species must be trimmed when the plant enters its dormancy period in late Autumn/early Winter. It is important to trim at this time only, as if cut during growing period, the plant will bleed a white sap that can lead to the plant being open to diseases. We also recommend you do not leave your Rowan hedge to grow exceedingly on its own, and instead give it a trim yearly to retain its strength and shape.
If there is any dead wood, be sure to trim back to the live growth at any time during the year. This will encourage the plant to grow back strong and healthy, with better berry and blossom production, in the following Spring.