In general you should try to wait at least 24 hours as a lower bound before accepting an answer - there is no upper bound and it's completely your choice; I personally go with ~1 week
There are many regulars on WorldBuilding.SE living all around the globe in different timezones. To give everyone a chance to look at your question you should at least wait 24 hours before accepting an answer.
The reasons mainly involve the quality and amount of answers you get.
Some people are discouraged when they see a question already has an accepted answer - the OP found the solution to his problem already, so why should I care and try to help him if he doesn't need any more help?
Furthermore people check out the question and the answers. They check whether the given facts make sense or whether some details need more work. This helps to increase the quality of the answers you receive.
All in all nobody can force you to accept an answer or not. It's completely, absolutely, totally your decision and yours alone when to accept, what to accept and whether you want to accept at all or not.
Relevant Meta discussions:
Please wait at least 24 hours before Accepting an answer
Is it better to accept an answer that's not quite what you were looking for or leave a question unanswered?
Let's be careful about accepting answers early
Should moderators mark a high voted answer as the accepted answer after a while?
Can I choose two answers for my question as the accepted answer(s)?
There are no special indicators about when a question will not receive any attention anymore
This depends on a lot of things.
Was it in the Hot Network Questions?
Did you post it on the weekends?
Is it referenced in other questions?
Did you or someone else put a bounty on it?
Did someone revive an old question with an edit or a new answer?
Are there already good, in-depth answers?
Did you recently edit the question?
Was the question put on hold and later reopened?
Are there new comments asking for clarification?
Is the view/vote count already pretty high for the type of question you are asking?
Just wait at least 24 hours and decide when you think nothing is happening anymore. Maybe a week? After two days or so you get a little message on your question tab, but in my personal experience I've mostly waited at least a week. Sometimes longer if one or more of the things above were true.
But, again: if you haven't got a satisfying answer you don't have to accept an answer. Nobody can force you or tell you what's right about accepting. These are just a few tips to increase the visibility of your question and thereby increase the amount and quality of the answers you receive.