Chapters generally take a day or two to be approved. For User created titles max is 7 days (?)
If your chapter hasn't been approved in longer than two days, go into https://mangadex.org/settings , double check that unavailable chapters is set to "Show (for tracking purposes)", then open your profile page to see if there are any unavailable chapters uploaded by you. If there are, that means your uploads were successful and are pending approval by staff. If there aren't any, your upload was either not successful or rejected. Type !up if you believe it was an upload problem. If it wasn't an upload problem, contact staff to check why your chapter was rejected.