##Closest I can think of RAW is the passage on diplomacy's Retry.

Try Again Optional, but not recommended because retries usually do not work. Even if the initial Diplomacy check succeeds, the other character can be persuaded only so far, and a retry may do more harm than good. If the initial check fails, the other character has probably become more firmly committed to his position, and a retry is futile.

Now, this isn't rules-talk, but if I were to interpret it, it'd be 'followup checks are made at a penalty. If a check doesn't improve attitude at all, no retries can be done'.

Now, if your player wants to take his time about it, I'd say allowing an exception for taking 20 to be the way to go. While diplomacy isn't a normally take-20 skill, this is exactly the situation that would seem to call for it.

Closest I can think of RAW is the passage on diplomacy's Retry.

Try Again Optional, but not recommended because retries usually do not work. Even if the initial Diplomacy check succeeds, the other character can be persuaded only so far, and a retry may do more harm than good. If the initial check fails, the other character has probably become more firmly committed to his position, and a retry is futile.

Now, this isn't rules-talk, but if I were to interpret it, it'd be 'followup checks are made at a penalty. If a check doesn't improve attitude at all, no retries can be done'.

Now, if your player wants to take his time about it, I'd say allowing an exception for taking 20 to be the way to go. While diplomacy isn't a normally take-20 skill, this is exactly the situation that would seem to call for it.