Get time elapsed in a bar

Is there a way to send a command once a certain amount of time has elapsed in a bar? Also, can I get the bar duration?

If I'm reading right OnBar() just works at the start and I've been unable to find an efficient workaround. The only thing that comes to mind is telling the function to work every X time but there has to be a more elegant solution that doesn't tie me to a specific bar duration.