DHW cylinder stat wiring

I want to add a timer/programmer to the domestic hot water control on my ce ntral heating. The system uses Sunvic "MOMO" type valves so at each thermo stat there is a "common" and "open" and "close" terminal. I have managed t o get the central heating working on a simple programmer and double throw t ype thermostat but the hot water circuit is at present controlled by a sing le Honywell cylinder stat which annoyingly often switches on during the nig ht so I need to put a timer in this circuit to stop it coming on at night a nd gain more control over the water heating. The Honeywell cylinder stat has three wires going to it RED (common) YELLOW (1) and BLUE (2) . I thought initially I might be able to simply interrup t the supply with a single pole switch on/off timer in the RED common wire but thinking about it I guess it might cause havoc with the motorised valve s especially if it switched off half way though an open/close action. I hav e a double throw mechanical time switch which I thought might do the trick but I am uncertain of how to put it in the circuit. I only have access to the three core cable going to the cylinder stat. Can it be done?
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On Mon, 25 Nov 2013 10:39:31 -0800 (PST), snipped-for-privacy@gmail.com wrote:

I /think/ this should work? :- http://www.flickr.com/photos/13629865@N03/11065575824/
Live/line to your timer common and "Day" timer contact to stat common gives normal wiring (as your thought to simply interrupt the supply).
Add wire from "Night" timer contact to whichever stat connection that turns the valve off.
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