They’re molecular-clock estimates with a real margin, best read as “at least this old” rather than exact years. Each dated branch shows the age of the most recent shared maternal ancestor of everyone on it, drawn from published scientific estimates. Some branches don’t have a published age yet — where that’s the case, we leave it blank rather than guess.
How precise are the age / TMRCA dates?
These are molecular-clock estimates with a real margin — best read as “at least this old.”