I've seen some comments in the original question that suggest the question can only be answered by a developer. This would make the question off-topic for the developer intent reason:
Speculative questions about developer intent, with respect to both mechanics and narrative
There is a good argument for this question being "developer intent". The underlying reason for the rule is to stop questions that can only be answered by a developer. In this case, it has been assumed only the developer can say why the beta was closed later than advertised.
However, I would like to make some points that would suggest we, as gamers, can provide some expertise as to why the beta closed later than the time you provided:
- Timezone differences (as already mentioned in the comments for the original question)
- The development team being unable to close active servers (does anyone remember the Halo 2 server closure on the original Xbox?)
Yes, sure, identifying possible problems is speculative, but there are plenty of examples in the past where some game doesn't ship on time, or some server doesn't close at the exact posted time.
You'll probably find there won't be a great appetite for getting this question re-opened because at best it is borderline speculative, and already obsolete. If someone provided a good and/or correct answer right now, how would this help you?