How far apart is it okay to set thermostat during night and day
The advice is for the purpose of avoiding frozen pipes.


The larger the difference in thermostat settings, the longer the heat will be off.
The longer the heat is off, the bigger the temperature differences between the cold parts of the room and the warm parts of the room.
Your thermostat is likely to be in a warmer part of the room (inside wall, at eye level) and your pipes are likely to be in the cold parts of the room (in the walls or on the baseboards, often down low).


I had frozen pipes when I was using a room the night before and had the heat up around 70.  Then the night time setting of 45 degrees took effect.  The baseboard radiators froze before the heat at the thermostat reached 45 degrees and kicked the heat on.  This was on a night when the temperature was below zero.  I also had some cold air coming in directly behind that radiator. (I have since installed additional insulation there.)

My plumber offered to install a special controller on my boiler that circulates some hot water through the radiators every half hour or so even when the thermostat doesn't call for it.  This type of setup will allow wider temperature swings with less risk of frozen pipes.  I opted not to do so because the controller itself was expensive.  Adding some insulation and having a slightly higher night time temperature were easier.

To avoid frozen pipes:


Keep the night time setting well above freezing.  At least 50 degrees.  My plumber recommends at least 55.
Avoid large temperature swings so that the corners of the room don't cool down to below freezing.  I wouldn't worry about the 10 degree difference that you are proposing, but a 20 degree difference is more worrying.
Put the heat on "hold" if the temperature outside is going to particularly cold that night.