Time Engaged Tier refers to the term, Time Engaged, along with its tiers.
Tiers are every 20 seconds:
0-19 seconds
20-39 seconds
40-59 seconds
60-79 seconds
80-99 seconds
100-119 seconds
More than 120 seconds
For example, if a user spends 30 seconds of engaged time on your website, they would be in the 20-39 seconds tier.