Formula To Return Average Days Between Two Dates In A Given Month?

I have a workbook with two sheets. The first has a list of job positions open, columns designated to stages in the employment process and in these columns, my staff enter the dates that they completed a particular stage.

"Position | Date Opened | Stage 1 | Stage 2 | Stage 3 | Stage 4"
Pos 1 | 01/01/2014 |02/01/14|03/01/14|07/01/14|09/01/14

This has a great number of entries and they are increasing and decreasing every day depening on the amount of jobs available.

On the second sheet, I am trying to set up a table which shows the average working days it is taking to complete each stage, divided into the months in which the job position was opened (i.e. for positions opened in january, the average completion working days for stage 1 was X amount of days etc...)

I have tried using =IF(AND(Logical, Logical),TRUE,FALSE) but this doesn't return any info as the logicals will always be false. I tried the OR function, but that requires only one of the criteria to be true to return a value. What I need is for the formula to return a number of days between two dates, ONLY if the opened date falls in one month.