Ann: Finbar Announces Activation of On-Market Share Buy-Back, page-2

Anyone familiar with buy backs able to specify the rate at which the buy back is conducted? I assume that the buy back is just done at current market prices when the relevant responsible broker/firm chooses to snap up stock in the company? Basically acting as a buyer support??

Or are there preset levels to work out when a buy back program will kick in , and how much stock/total value will be spent in the buyback at each buy parcel? Obviously the total can be up to 10 million shares.... pretty decent amount of shares.