There is no rule regarding this at all. You're not even obligated to ask for OP's preferences (though it's a courteous thing to do!)
In my opinion, you should go ahead and fill the prompt however you want as long as it doesn't have any of the OP's DNWs (if they were specified). Regarding the amount of time you should wait: that is 100% up to you.
Re: Not sure if I should ask a mod or general discussion
In my opinion, you should go ahead and fill the prompt however you want as long as it doesn't have any of the OP's DNWs (if they were specified). Regarding the amount of time you should wait: that is 100% up to you.