In his book How Jesus became God Dr. Ehrman argues that the three day motif we find 1 Corinthians 15 and in each of the gospels was a later development of Jesus tradition and was a result not of remembering events but of exegesis–that is, someone or someone(s) decided they needed a more precise timeframe and searched their bibles until they found a number.  That they decided upon the number three has led historians to speculate that Hosea 6:2 was the source for this decision.

I find this theory implausible.  It is easy enough for us, after the timeframe has been chosen and handed on, to comb through our bibles till we find a verse that resonates, but that is not the position the originators of the tradition were in.  They had nothing, perhaps not even their bibles. Hosea 6:2 is about apostate Israel, and the number three is hardly eminent among the biblical numbers.  Given the resurrections early associations with New Creation (Gal, 2 Cor.) one might think seven a more promising candidate.

I find it far more plausible that the timeframe was determined for them by the actual appearances (whether real or pathological) and if the clause “according to the scriptures” refers to the timeframe, then maybe they combed through their bibles till they found a passage that had the number three and roughly fit the context.