The problem here is we can’t conveniently measure vo2, and so it requires triangulating with power, heart rate, and perceived exertion. Or using WKO4 and using its estimates based on your 90-day power duration curve.
Billat has an interesting study about “hard start” vo2max efforts: https://www.researchgate.net/publication/228104183_The_sustainability_of_VO2max_Effect_of_decreasing_the_workload and if you look at Figure 1, subject A has ftp of 300W and did 400W for about 90 seconds and then went below FTP for most of the remaining 14 minutes, while still maintaining the aerobic/vo2 level of doing a constant 400W for 4 minutes.
In other words, around 16 minutes of max aerobic effort in a single “interval” instead of 4 minutes. BUT you need a vo2 mask to know you are operating at max aerobic because subjects B and C reduced power to ftp and slightly above ftp. Would love to get one of these masks for vo2 workouts: https://vo2master.com but its the cost of a fancy new carbon bike.