Starting at a high temperature of around 49C for one hour is meant to speed up the culturing quite significantly. They recommend lowering the temperature to 30C after one hour to prevent whey separation and lumpiness.
My yoghurt maker which only had small pots of under 200ml used to complete in about 3 hours. The temperature was around 43-45C. However the temperature started getting very hot, going up to 60C. They have crap temperature regulation. It was too hot so I had to take it apart and adjust the heating element, bending it in the centre where the heat was highest. Unfortunately it lowered the temperature a bit too much and it now only gets to around 38-39C and the time to completion has significantly increased to around 7 hours
See the link for details of how they recommend doing it. There is other yoghurt fermenting info in the 2nd link.
I do have a dual input 2 pin digital thermometer which can use different types of temperature probes such as T & K types and many others that I cannot remember. My probes is a T types for maximum accuracy at the required testing range. It cost me as much as the meter and the reason why I spent so much was the handle which allows the probe to be rested on the worktop where it rests on the handle with the probe parallel above the worksurface. The one that I had before, a fairly cheap one I had to put in a glass but I had to mess around sterilizing the glass which was a bit of a nuisance.
I would like to build a fermenting device with a STC-1000 temperature monitor with a custom firmware which was made to ferment beer. The custom firmware allows profiles to be created where the temperature can be programmed to change after set periods, either minutes or hours depending upon the firmware. So it could be programmed to work at 49C for one hour and then 30C, if what the site says is best, for the remainder. However I have doubts about 30C as it is well below the ideal temperature for many bacteria which tend to be around human body temperature.
ATM I am stuck finding a chamber which I can use. I have thought about it but I have not come up with anything which I like. Making one from a metal such as stainless steel would be difficult without a press to bend it cleanly. Aluminium would be easier but I don't like aluminium even though it would conduct well and not come in contact with the yoghurt. A plastic vessel/chamber I have not found anything suitable so far. A lid is required, preferably clear and it all has to fit together which makes it very difficult to find. I did have an idea of using a thermoelectric mini fridge but did not like the price for new ones and finding a faulty/none working one are not really cheap enough.
http://brodandtaylor.com/custard-style-yogurt-recipe/http://brodandtaylor.com/yogurt-recipes/