Can anyone explain, how LTI mass update is triggered? (I know how to set the interval).
Would it be possible to do mass_update() at predetermined time(s)?
I must admin I've never actually done this. Take a look at the scripts in /opt/webwork/webwork2/bin. Many of them execute WeBWorK operations from the command line. It's likely that this can be done with wwsh, which is designed for exactly this sort of thing.
For more detail someone with more experience with these things will have to chime in.
It would be tempting to call mass_update() from a script fed to wwsh. However it looks like an HTTP request from LMS to WeBWorK is first needed in order to construct a pass-back HTTP POST to LMS...
That is probably the reason mass_update() is called from ContentGenerator :)