Page 236 of Thomas Dozeman’s commentary on Joshua says that 6:25 is an etiology to explain how the “clan of Rahab” continued to live among the Israelites, and he refers to Martin Noth’s view that the Rahab story of Joshua 2 was subsequent to the etiology. The NRSV translates 6:25 as: “But Rahab the prostitute, with her family and all who belonged to her, Joshua spared. Her family has lived in Israel ever since. For she hid the messengers whom Joshua sent to spy out Jericho.” It has a footnote indicating that “family” is actually “she” in Hebrew. Robert C. Dentan includes the following annotation for the verse:
Ever since may show that people who claimed to be descendants of Rahab lived in Jericho at the time that this story was composed; it thus served to explain the survival of some Canaanites and their continued presence in Israel.
With regard to time markers like this as a whole, the Pentateuch has many: Genesis 12:6, Genesis 13:7, Genesis 36:31, Genesis 14:14 (cf. Judges 18:29), et al. Conservative exegetes generally dismiss these as later additions to bring the text up to date, but deny that it bears on the dating of the text in general.