NetSuite saved search for when the task start date is in the same month, then sum together the task hours and divide by project total task hours

Question

We recognize revenue by hours associate with tasks % complete. I need to create a NetSuite saved search formula that groups together task start dates by month, then adds together the associated task hours by month, then divides that by the total project task hours, resulting in % of task hours projected per month by project.

CASE WHEN {projecttask.startdate} = MM then sum{projecttask.custevent_eggstart_estimated_work} / {custentityegg_totalestimatedtimestore}

I need the correct formula to group together the project task start dates by month and then add the associate hours per task by month.