1
general::
Far advanced; also, too far advanced. For example, It's late in the day to change the kitchen layout, since we've already ordered the cabinets, or It's a bit late in the day for apologizing. [Late 1700s]
American Heritage Idioms
2
general::
Phrase(s): late in the day
Fig. far along in a project or activity; too late in a project or activity for action, decisions, etc., to be taken. • It was a bit late in the day for him to apologize. • It’s late in the day to try to change the plans.
McGrawhill's American Idioms And Phrasal Verbs