According to a tweet put forth by PlayStation Europe the PlayStation Network will undergo maintenance on Monday the 9th, and Tuesday the 10th of December between the hours of 16:00 and 00:00 GMT.
During this eight hour period users who have not signed in prior – and thus cached their authentication – will likely be unable to access the PlayStation Network at large.
Heads up > There will be Network maintenance on PSN – Monday 9th/Tuesday & 10th Dec between 16:00 and 00:00 GMT. Thanks for your patience.
— PlayStation Europe (@PlayStationEU) December 6, 2013