Final answer:
The horizontal branch length in a phylogenetic tree indicates the order in time of evolutionary events, not the length of time that has passed.
Step-by-step explanation:
In a phylogenetic tree, the horizontal branch length indicates the order in time of evolutionary events, not the length of time that has passed. A longer branch does not necessarily mean more time has passed, and a shorter branch does not mean less time has passed, unless specified on the tree diagram. The horizontal branch length simply represents the sequence in which traits or species evolved.