454 letters / CVs a day is doable if they employ computer software to eliminate those who go over word count, those who make more than x spelling mistakes etc. By the time the software has filtered out half of those, that leaves 2 minutes for someone to read the covering letter and another person to read the CV... Possibly longer depending on how many people they have in their "talent team".
I'm surprised that it's only 5000 applicants. When Scotrail recruited last time for 100 posts, they were inundated with over 22,000 applications. Given the fact this recruitment is for 6 stations UK wide, I'd have expected a lot more. I'm not complaining, mind you ??????