I suspect it might not work - and may actually increase costs. During the off-times, you're going to get cold (or cooler). Thus there may be a temptation to turn up the stat a bit to compensate. So now the house will heat up a bit warmer during the on periods and increase overall losses.
That would be my 'gut feeling" anyway.
Something else worth looking into is whether your system lends itself to splitting the upstairs heating from the downstairs (by adding a third zone valve, programmer channel, and room stat). If it does, then you could leave the upstairs heating off except for a short time around getting up and going to bed times - and thus save the losses that would otherwise be occurring during the day when (I assume) you won't be upstairs.
If the system layout doesn't lend itself to that, then another option is an electric setback option on the TRVs. I believe these can be bought (at a price), but over on another forum I know people have been experimenting with adding a resistor (heater) strapped to the TRV sensing element to fool it into thinking the room is warmer and turning down accordingly.
However, these will start needing wiring to each TRV etc, and costs could quickly mount up.
Of course, some people remember the days when keeping warm meant investing in warm socks, slippers, and cardies. I'm young enough not to have lived in a house without central heating. ON the other hand, my parents tell me stories of scraping the ice off the inside of the windows in winter.
