How to sum PivotTable Data using two dates and a ID reference

[JonathonTait]

I have a large pivot table data set that shows me the amount of sick days for each staff member over a set period of time. You can see the dates and the staff ID across the top. I am needing to sum the amount of sick hours between to dates based on the staff ID. The two dates will vary depending on the staff member.
Can someone help me with a formula that can extract that info.

See reference pivot table below;
I would like to reference the Staff member ID and then have it sum the sick hours based on the dates I have selected.