Hi Tomek
I can only offer my observations for the EC135 and 145T2 which as flying Bull and Skadi point out have a requirement for the power assurance check on an hourly basis but both also have a requirement for trend monitoring to be established if operated in cat A (class 1). The frequency isn't specified,to the best of my knowledge, but daily seems sensible because it is much easier for us more forgetful pilots to remember to do something every day rather than to note when the aircraft is going to hit its next ten hour anniversary!
For the EC145T2, the power assurance check is exactly the same as the trend check i.e. both are carried out at 70% torque (not very obvious if you follow the on screen instructions of the Helionix which just call for flight above Vy!)
Cheers
TeeS