Is this OK with ordinals in a formal report?
On December 23rd, 2012, at 5 pm, Mary Smith resigned. On December 29th, Bob Hellwig took over her position as senior vice president.
Yes. Of course, some companies or institutions might have in-house styles that they stick to in all reports.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.