Going to preface my thoughts on the fact that I only have VPR at 90, so I don't have firsthand experience at 100. My understanding from a few people that I know who main viper is that the only time the 20s timer is much of a concern was if you planned on doing 2 Reawakenings in a row (with more lenience) or 3 in a row (very tight lenience); but that ultimately the way the class pilots itself you almost never have to actually think about the timing of it. That seemed pretty in line with my understanding of the job at 90, maybe with the exception of the boss going invulnerable right before you would use Reawakening?