Hi,
The time spent field on the request will be updated, only the time of closure of the request. Hence, there is no option to calculate the time spent for pending requests.
In case, if the technicians use the work logs, you could run a report using the 'Time spent' module under the custom reports in ServiceDesk Plus to generate the required report.
Login to ServiceDesk Plus, go to Reports > Custom report, choose 'Time Spent' module and proceed to report wizard. Choose the required columns and run the report.
Regards,
Stephen