The phrase "most arrival" typically refers to the event or time when the greatest number of people or things arrive. Some potential synonyms for this phrase could include "peak arrival," "maximum influx," "highest entry," or "prime entry time." Depending on the context, other synonyms could be used to convey a similar meaning. For example, in the context of air travel, "rush hour" or "peak travel time" could be used to describe the period when most flights arrive at an airport. Ultimately, the choice of synonym will depend on the specific context and tone of the writing, as well as the writer's personal style and preferences.