Apart from the fact that the dating of Job is notoriously difficult, I would be suspicious towards a bible plan that claims to be chronological and places one book after the other (which I guess from your post). For example, Ex. 15, the song of Myriam, is generally considered to be much older than the surrounding text.
Another example: the book of Isaiah was written by at least three different authors over several centuries, and later on different parts have been assembled into one book. Some scholars even want to divide Proto-Isaiah, the first part (ch. 1-39), in six. Also, the four songs of the servants may have been a separate book before. 
The Pentateuch is considered to have been composed from different sources, from as early as 1000 BCE till around the Babylonian exile, c. 500 years later. Several passages seem heavily fragmented to the point that even if all different sources could be dated precisely, a chronological bible plan would mean having to skip from verse to verse.
Having said that, in the Talmud it is claimed that Moses wrote Job (recall that traditionally, Moses is considered to be the writer of the Pentateuch). See for example :
It is the opinion of many of the ancients that this history was written by Moses himself in Midian, and delivered to his suffering brethren in Egypt, for their support and comfort under their burdens, and the encouragement of their hope that God would in due time deliver and enrich them, as he did this patient sufferer.
As far as I know, this is not considered a viable option in current-day exegesis, but it may explain why your bible plan is organised this way.
: Debel, Eén naam, een veelzijdig boek: Jesaja te midden van de profetische literatuur. Ezra 2014 (Dutch).
: Matthew Henry, An Exposition, With Practical Observations, of The Book of Job.