Calculating Open Days field and stopping with status change
Counting days without explicitly storing the start date would require some kind of scheduled task to count them.  This is not trivial to implement and not recommended.

I would suggest storing the date when opened and then doing a date diff between the start date and the current date to work out the number of days (including the appropriate rounding).  I would suggest that it might be a good idea to also store the closing date.

Edit:

When the item is closed you have two options to work out/read the days opened in the future:


You can store both the start date and the close date and do a datediff between them when you need to know the days opened.
You can store the days open explicitly when you mark the item as closed.


I would recommend 1 as it is more concise.

Edit2:

To fully explain point 1.  Basically you would use the datediff function and compare the start date to the current date, while specifying days (d) as the required unit.

In an SQL select query this would look something like:

select 
    datediff('d',table.StartDate,date()) as OpenDays,
    table.Status
from table


The date() function returns the current date.

Microsoft Access Help on DateDiff