Stop Counting Function with NETWORKDAYS plus Conditional Formatting?

Hello, I am stumped - have seen some info on this forum related to the above, but cannot piece it together to have it work for me. I just can't get the formulas to work. Here is the scenario - I have a worksheet in Excel 2010 which tracks each step of the hiring process along with a proposed Enter On Duty (EOD) date, and an actual EOD date.

J4 - Populated w/Projected EOD Date
O4 - User types in date paperwork submitted to HR to start hiring procedures
X4 - User types in the actual EOD date
Y4 - Countdown to Projected EOD Date
Z4 - Status of Hiring Action - this block turns yellow (in-progress) or green (completed) based on whether or not just O4 is filled in (=in progress), or green (=completed) if both O4 and X4 are filled in. This was done in conditional formatting with formulas based on Blanks.

1) When user inserts date in O4, I've got a formula plugged in that automatically populates a date based on a 100-day timeline in J4. That works fine. Formula is: =IF(ISBLANK(O4),"",WORKDAY(O4,100))
2) In Y4, I have a formula that starts a countdown and indicates how many days left until the Projected EOD Date is reached - that seems to be working fine - =IF(J4="","",NETWORKDAYS(TODAY(),J4)). I included in these functions for cells to remain blank until ref data is entered.

3) Here's the issue: When the user types in the actual EOD date in X4, I want Y4 to stop counting the days, and keep the # of days number in the column whether it is a positive or negative #. X4 additionally has Conditional formatting built into it whereas the cell turns red if the date entered exceeds the date in J4.

I'm just lost on how to get XY to do what I need. I'm desperate for an answer. Also, I realize i have formulas for both WORKDAY and NETWORKDAYS above, but it seemed from my research they were each capable of only certain things - is that correct? Thank you so much - Chris

Hi, I think it may now be figured out without using VBA. I have no issues w/VBA, it is just that my coworkers would not understand it should a change need to be made and I was not there. I could not upload a copy of sheet as it is sensitive, and is a fed govt document. However, here's how it worked outin Y4, changed the function to:
=IF(ISNUMBER(X4),NETWORKDAYS(O4,X4),IF(J4="","",NETWORKDAYS(TODAY(),J4))) - from what I can tell, I think it is working OK. It is stopping the countdown when the user enters a date in X4 (Actual EOD Date), and then calculates to what I need. I am not sure if there are any other alternatives, but it is definitely better than where I originally started! Thank you-Chris