When timesheets are used to update task time worked, you need to submit and approve the timesheet for the corresponding time period in order for the time period in order for the Actuals to apply against the Task. Bear in mind that once a timesheet is submitted, it is effectively locked unless declined or re-opened by an approver or supervisor, so your users should only submit their timesheets at the end of the timesheet period once their time is complete.
However, any time you report via a Task update should appear on the Timesheet for the time period for which the hours were reported. If you are not seeing time added at the Task Update level reflected on the timesheet, check that the hours worked were reported for the correct date and that the timesheet has not been submitted.
Although not an ideal way to monitor task time actuals, you are also able to export timesheet data via the Timesheets tab, which includes task time whether it's been submitted/approved, so you can monitor this time between timesheet submissions.