It’s generally approved around 4 months from the date IRCC receive the application. So if the application has been returned, the countdown begins again from the date they receive the amended application.
You’re not the only one caught out on the OWP insufficient fees issue, so anyone who’s had this issue before you, and has since had their OWP application approved, will hopefully be able to provide an update on timescales for you. There may be some expedited process for those applications returned, however, IRCC does state that any application returned for any reason will be treated as if the initial application was never submitted. This is how some people lose valid status, as they rely on implied status, but implied status ends when an application is returned. It’s always prudent to extend your visitor status, just as a back up.
Hopefully you won’t have to wait too long. Good luck.