A system for activating a blowout preventer of a wellsite, the blowout preventer comprising rams (115a,b) sealingly positionable about a tubular of a wellbore at the wellsite, the system comprising: a circuit operatively connectable to the blowout preventer, a cylinder (246,246a); a piston (248,248a) slidably positionable in the cylinder, the piston having a piston stroke extending between a retracted position and an extended position; characterized in that the circuit comprises: a sequencing valve operatively connectable to a first of the rams; and a supply valve operatively connectable to a second of the rams; and an activator operatively connectable to the circuit, and the activator comprises: a trigger valve (238,238a,238b) operatively connectable between the cylinder and the circuit, the trigger valve comprising a trigger (474a,b) to selectively pilot the circuit; and a timing adjuster (250,250a) engagable by the piston, the timing adjuster adjustably positionable about the cylinder to define the retracted position of the piston stroke whereby a length of the piston stroke is adjustably defined and wherein the piston (248,248a) is driven by passing fluid from a first set of rams to the cylinder (246,246a) via the circuit. a circuit operatively connectable to the blowout preventer, a cylinder (246,246a); a piston (248,248a) slidably positionable in the cylinder, the piston having a piston stroke extending between a retracted position and an extended position; characterized in that the circuit comprises: a sequencing valve operatively connectable to a first of the rams; and a supply valve operatively connectable to a second of the rams; and an activator operatively connectable to the circuit, and the activator comprises: a trigger valve (238,238a,238b) operatively connectable between the cylinder and the circuit, the trigger valve comprising a trigger (474a,b) to selectively pilot the circuit; and a timing adjuster (250,250a) engagable by the piston, the timing adjuster adjustably positionable about the cylinder to define the retracted position of the piston stroke whereby a length of the piston stroke is adjustably defined and wherein the piston (248,248a) is driven by passing fluid from a first set of rams to the cylinder (246,246a) via the circuit. a sequencing valve operatively connectable to a first of the rams; and a supply valve operatively connectable to a second of the rams; and an activator operatively connectable to the circuit, and the activator comprises: a trigger valve (238,238a,238b) operatively connectable between the cylinder and the circuit, the trigger valve comprising a trigger (474a,b) to selectively pilot the circuit; and a timing adjuster (250,250a) engagable by the piston, the timing adjuster adjustably positionable about the cylinder to define the retracted position of the piston stroke whereby a length of the piston stroke is adjustably defined and wherein the piston (248,248a) is driven by passing fluid from a first set of rams to the cylinder (246,246a) via the circuit. a trigger valve (238,238a,238b) operatively connectable between the cylinder and the circuit, the trigger valve comprising a trigger (474a,b) to selectively pilot the circuit; and a timing adjuster (250,250a) engagable by the piston, the timing adjuster adjustably positionable about the cylinder to define the retracted position of the piston stroke whereby a length of the piston stroke is adjustably defined and wherein the piston (248,248a) is driven by passing fluid from a first set of rams to the cylinder (246,246a) via the circuit.