If you use heightSpec: "Parent100Pct" the Scheduler will use the available space, i.e. 100% of the parent element. It requires that the parent element height is set properly (either using height or absolute position with top/bottom).
It also detects changes of the parent element and adjusts the height automatically.
In addition to that, you can request a manual height detection by calling show():
https://api.daypilot.org/daypilot-scheduler-show/
Another option is to set the height manually in pixels (it forces heightSpec: "Fixed"):
https://api.daypilot.org/daypilot-scheduler-setheight/
You can also use update(). The options listed above would be slightly more efficient but you don't have to be afraid of using update().