Before we get into this, let's recap how TimeHero automatically plans tasks:
TimeHero looks at a task's assignee, work estimate, start date, due date, any links to other tasks/events, and priority. It also looks at the start date and due date of the project where the task is saved.
It then attempts to schedule the task in continuous one block inside the assignee's work hours. This block is as long as the work estimate (e.g. 2 hours). TimeHero will try to schedule the task before its due date, before the project's due date, and according to any links you have set.
So if a task isn't planned, it could be because:
The task's assignee doesn't have their work hours set
There's no work estimate on the task
The project does not have a start date
The task is linked to either an event with no date set, or a task which isn't planned yet
The task's work estimate is longer than any block of free time in the assignee's calendar (e.g. a 9 hour task, and the assignee only has 8 work hours per day)
To help with that last case, TimeHero will try to automatically toggle Task Splitting when long tasks are created. This splits the task into smaller chunks, which will then schedule around other tasks, other events, and over multiple days. To toggle Task Splitting manually, open the task to see the details panel and click the toggle next to "Task Splitting:
You can also click on the blue highlighted time (in this case 1h) to change the minimum time that the task can split into.