I’m signed up for a 24hr MTB event as part of a 5-person relay team. Laps are expected to be about 1.25hrs, on relatively fast rolling trails. The team is going for rotating laps so I’ll be on for ~1.25hrs then off for ~5hrs, 4 times.
Is this Cross-Country Marathon?
Thanks in advance.
Hey @rshelmerdine, welcome to the forum! 
This is a good question. 
I’d say that it really depends on the type of effort you’re expecting to have to produce. If you think the race will include mostly race tactics and hard efforts, then Cross-Country Marathon could be a good choice.
If, instead, you think it will mostly be a race of attrition and you plan on riding at a pace that you’ll be able to sustain for the entirety of the event, then something like Gravel or Gran Fondo could be a good option as well.
The XCM plan has a bit more sharp efforts included and race specificity, such as hard starts, so again, if you think you’re going to race this event like you would an XCM one, then that’s probably the best choice. If you’re planning to ride this more like a really long ride, then I’d go with Gravel or Gran Fondo.
It’s a bit tough because you’re all rotating through, so each lap isn’t that long, but you’ll rack up riding time throughout the day without a ton of real recovery between laps.
Let me know if this helps and if you have any other questions! 
Thanks! I hadn’t considered Gravel or Gran Fondo plans, but yes I definitely see myself riding this consistently, not in explosive efforts. I’ll look them over.