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 for too long, however, as you don't want the roots to become root bound.
The Box hedging will only need a trim once/twice a year, and we recommend a well-rotted, or mulch, compost to keep your Box hedging in the best condition, along with the use of seaweed fertiliser and root grow as a feed in the spring. In terms of pruning, you can prune back young box plants by up to a third within their first year of growth (this is to encourage a dense, bushy new growth). If you already have a bushy hedge, then your Box can be pruned once/twice a year only, within May and August time.