Link WHERE field in group-by query to main report?

[HeatLyn]

I would like to link many sub-reports to a main report but one of the items (in the sub-report queries) is a parameter which is a WHERE statement. Does anyone have any ideas on how I can get around this? Below is an example (* represents the links- how would I link the time_stamp field when this field cannot show up in my group by/count query)? Thank you for any help you can give me.

Main Report Fields
* program_code
* time_stamp

Sub Report1 Fields
* program_code
gender
count_of_gender

Sub Report2 Fields
* program_code
County
Count_of_county