When do Tickets normally go on sale? - a newbie question

Hi All

Newbie here - so my apologies if there are posts already answering this question. (I had a look and couldn't see anything - but can't rely on my eyesight!)
Me and friends are muchly lookin forward to coming to GB11 and this will be our first time.
Does anyone know roughly when tickets go on sale ? We would like to make sure we've got the money in place to buy the tickets!

Thanks