Wouldn’t it offset one passengers CO2 for a whole day and not just a single passenger passing by? I’m sure that’s what you mean but the wording is a bit confusing.
It sounds like it would offset one person staying in the airport for a quarter of a day, yes. Though, with how many people pass through an airport, it means that this would do, instead of almost nothing, four times almost nothing.
Really it's about the average occupance of the airport over 24h, which is going to be far greater than 0.25.