Mentally, not physically (probably)
Drilling out ERG controlled watts at threshold for 20 minutes x 2 takes some practice and training no? Which is why you normally build up to them 3 x 10, 3 x 15 etc?
Well FTP is only 95% of your max for 20 mins so you should be able to hold it for an hour solid.
If you can't then it's not a true reflection of your fitness.
And if it's your hour power, 2x20 shouldn't be that difficult.
Mentally, not physically (probably)
Drilling out ERG controlled watts at threshold for 20 minutes x 2 takes some practice and training no? Which is why you normally build up to them 3 x 10, 3 x 15 etc?