Something that will hold up the processing of a return is this ... if you submit your return before the IRS has received and processed your tax reporting forms received from your employers and other payers which show federal withholding on them. Until the IRS can confirm the withholding from those sources is the same as what you claimed on your 1040 they will hold your return in the processing pipeline. Just because you got the tax form doesn't mean the payer filed it yet ... many payers will hold the filing with the feds until the last minute to allow the employees to report errors on the forms. This way they can make the corrections before they file the forms and save them having to file corrected forms which are a pain in the butt.
