From my years in software development, I think I can guess. The thursday deadline was promised as a result of a staff meeting two weeks ago where the developers asked for two more days, confident that all issues could be resolved. To be on the safe side you added 1 or 2 days. In the meantime the testing has revealed a huge hole that will take a week to even evaluate the scope of the problem, three days of detailed impact analysis and another week of coding plus a full re-test.