It seems there is no way to edit the calculation method to ‘TimestepFrequency’ … I used either a text string or number to change the default setting, but when I open the .idf file, it is still remaining as default…
Also all of my attempts to bypass this with the setString method are not working.
It may not be possible to set this property using OpenStudio SDK but I will keep looking. I can also ask the OpenStudio developers how this should be done.