There are a number of threads on this sort of topic already of course.
GCN’s Dan Lloyd is riding a 350km / 220 mile on 22 June 2025.
His specific training plan for the event has started in the last week or so (10 weeks, but he has a week of holiday in there, so 9 weeks really).
This video, from 24 April 2025, includes an overview of the training plan he will follow (from about 9’00" onwards)
4 cycling sessions per week, 6 hours per week
Tue & Thurs are 1 hour interval workouts: 10 x 1 min all out efforts with 2-3 minutes rest between
Sat is a 1h30m endurance ride “if you’re feeling good, start to introduce some intervals at threshold pace”
Sun is a 2h30m endurance ride “if you’re feeling good, start to introduce some intervals at threshold pace”
There is talk of a longer ride a couple of weeks before the event - half of the event distance / duration being mentioned.
And additional endurance rides if time and fatigue allows - protecting the Tue / Thurs interval days being a priority.