Mechanical plant extension timers, also known as “override timers” or “caretaker timers” within the BMS & HVAC industry. Totally mechanically driven by a clockwork spring, therefore no auxiliary supply is required. The moment the setting knob is turned pass zero to the set time required, the output contact switches, the timer will then start running back to zero. When zero is reached the output contact will switch back. If after the initial time has been set, it is required that the set time, or remaining set time needs to be lengthened, shortened or cancelled back to zero, the time setting knob can be turned without harming the mechanical mechanism. The timers benefit from a 16 Amp/250V AC1 changeover contact and is easily fitted to the front of a control panel via screw fixings, which are discretely hidden by the time setting knob. Four time range versions are available 0-15min, 0-60min, 0-6hrs, 0-12hrs.