Your climate in Istanbul is nearly the same as Cephalotus is used to near Albany, Australia. Just have a look at the climate table of temperatures for comparison:
Albany in °C: http://www.worldweather.org/185/c00356.htm#climate
Istanbul in °C: http://www.worldweather.org/014/c00047.htm#climate
Or if someone prefers Fahrenheit:
Albany in °F: http://www.worldweather.org/185/c00356f.htm#climate
Istanbul in °F: http://www.worldweather.org/014/c00047f.htm#climate
Daily maximum in summer is a bit higher in Istanbul than in Albany, but stays below 30°C in average. Daily minimum drops below 20°C in summer months. Looks good in summer half-year.
Daily minimum temperature stays above freezing point in average nights in winter.
Looks good in winter, too.
I'd perhaps close the lid of the tank in January and February to increase the temperature level a bit during these two months and prevent most of the frost, and in the hottest summer months I'd keep the plants only with some morning sun to prevent midday sun.
Well done - keep it up!
Unfortunately, in my area (Northern Germany) I can keep Cephalotus only from May until November outdoors and have to take it inside during the rest of the year because winters are too cold here. Cephalotus likes it chilly, but doesn't like freezing.