Given the intent and time of writing of Daniel, it is, of course, not necessary at all that the story would actually have any relevance to Nebuchadnezzar. Instead, Nebuchadnezzar is used as a literary device. Rather than being any kind of historical account, the story borrows elements from the Prayer of Nabonidus, but the story adds and changes various details for its own purposes.
In the broader context of Daniel, the significance of the ‘seven times’ actually alludes to the 49 (7 x 7) years from Jerusalem’s destruction (587 BCE) until the Jews were allowed to return to Jerusalem (538 BCE). The same period is referenced in Leviticus 25-26, and also corresponds to the ‘7 weeks’ of the 70 weeks of Daniel chapter 9.
Notably, the ‘jubilee year’ concept described in Leviticus falls not on the 49th year but the subsequent 50th year, corresponding to starting work on the temple foundations in 537BCE. Significantly, other than the oblique reference to the period from 587BCE until 537BCE in Leviticus (which scholars recognise was completed during the Persian period), the Bible never once mentions any year as a jubilee year, and there is no evidence that jubilee years were ever actually practiced.