Is there an option to filter out the tasks which does not have time recorded on them via Rest API call?
Clarity 16.x
It is possible to use Actuals (actualSum) field when you filter. If you filter for actualSum = 0 you should get Tasks that don't have any actuals with the caveat that those actuals can be coming from timesheet as well as manual transactions.
sample call: http://your_server:your_port/ppm/rest/v1/projects/5004001/tasks?fields=name,code&filter=(actualSum = 0)