A standard retort from JW apologists about the Jews returning from Babylon to Judea in 'only' 6 months after Cyrus' decree is that it 'wouldn't allow time for preparations'. This retort never includes any kind of breakdown of just how long it would take to prepare, nor does it account for the fact that the size of the group allowed for division of labour for the preparations. Instead, it is simply a fallacious argument from incredulity.Exact preparation times can only be speculated, but tasks
could be divided among teams for responsibilities such as leadership,
logistics, supplies, route planning etc, which would greatly reduce the
time required for overall preparations. So the claim that it would be
'impossible' is entirely unfounded, particularly for people who were highly motivated to make the trip. And some of the many Jews who remained in Babylon might also have helped with the preparations.
As far as the journey itself goes, covering just 25km per day (allowing for a comfortable 5km per hour with several rest periods) and allowing 3 rest days per week, the complete journey could be done in about 16 weeks (112 days), if taking the long route of about 1,600km as proposed by the Watch Tower Society rather than the more direct route of about 800km.
(According to Ezra 2:64 and Nehemiah 7:66, 42,360 people, plus 7,337 slaves [which is apparently fine] and inconsistent numbers of singers made the journey, but comparison of Ezra 3:2 with Nehemiah 8:1-2 shows one or both versions to be unreliable.)