Journal of the American Heart Association. 2018;7
The 2008 Physical Activity Guidelines for Americans recommended at least 150 minutes per week in cumulative bouts of at least 10 minutes of moderately-to-vigorous physical activity (MVPA) in order to reduce all-cause mortality. This translates to at least 30 minutes per day for 5 days a week of purposeful exercise (read HIIT), which very few mortals with hectic lifestyles can achieve.
This study, which tracked worn accelerometer recordings (eg Fitbit), is heartening. It suggested that the cumulative duration of MVPA correlated best with longevity, rather than the intensity of activities, or how long such bursts of activity lasted. All-cause mortality was halved by accruing more than an hour of MVPA a day, while the best result was achieved with about 100 minutes of MVPA daily.
So, there's no benefit with HIIT with regards to longevity, and you don't need to go beyond 100 minutes a day of cumulative MVPA.