This is getting confusing.
Never use form rules to auto edit the data for data that needs to change due to the simple passage of time. That is just not how Quick Base works for data that needs to change through the passage of time.
You may want to book some one on one help to get this all working.
The typical setup is that there will be a formula to calculate the Vacation Entitlement based on years of service and typically allowing for a manual override in case one person gets a different deal that the rest.
Manual overrides are done by having a new field for the manual override and then a formula field that will use the either the manual override if not null (be sure to check the checkbox to treat blank as null) for that override field.
Then there will be a summary field for the vacation time used which is a summary of vacation taken subject to the filter date is "during the current year".
Then a new field to subtract to give the remaining vacation available to be taken this year. There is no one needed to manually subtract the remaining vacation. That happens automatically.
