Is it permissible to include a condition in the marriage contract stipulating the wife's right to demand the prompt and deferred dowry at any time she wishes, and would this be considered a deferral for an unknown period that could lead to dispute, and does its ruling differ according to the country?

The wife can demand the prompt mahr (dowry) at any time she wishes. As for the deferred mahr, if it has a specified due date, the wife is not entitled to demand it before that date. If no due date is mentioned, then its due date is either death or separation. However, if the due date is unknown (e.g., the wife demanding it at any time she wishes), it appears that such a due date is invalid, and the entire mahr becomes promptly due.