The Deepwater Horizon blew up on April 20th, and sank a couple of days later. BP has been criticized for failing to report on the seriousness of the blow out for several weeks.
However, as a whistleblower previously told 60 Minutes, there was an accident at the rig a month or more prior to the April 20th explosion:
[Mike Williams, the chief electronics technician on the Deepwater Horizon, and one of the last workers to leave the doomed rig] said they were told it would take 21 days; according to him, it actually took six weeks.
With the schedule slipping, Williams says a BP manager ordered a faster pace.