I was filling out an application for” XYZ” position and the posting closed at 4:45 p.m. I was on the check for errors and submit page. Can I still be allowed to submit my application?

Our posting closes at midnight (12:00 a.m.) on the day the job is set to close so your example would not have been the reason you could not submit your application.  Our guess is that it was an issue with the browser you were using.  Once a job closes, we can no longer accept applications for that particular opening.  We encourage you to check frequently and apply to others openings that might be of interest.