Hi paul_kiss,
It is possible in R:TW, but it's, sadly, not as simple as in M2:TW. To change it advanced background scripting is required which is way beyond my humber R:TW modding knowlage. Fortunately, a highly esteemed modder has kindly created a mod which enables four turns per year, you can find it here, but for other timespans you will have to try playing with the files yourself. Sorry.