=SUMPRODUCT(SUMIF(INDIRECT({"1","2","3","4","5"... "31"}&"$A$5:$A$100"),C1,INDIRECT({1","2","3","4"," 5"..."31"}&"!$C$5:$C$100")))/3600

Where A:A is name column on each date tab wksht (name appears regardless if data is present), C1 is on Summary tab and holds name and C:C provides numeric data (seconds) on each date tab wksht...formula is on Summary tab...

Data is inserted each workday for the previous workday on each data tab, C:C has a formula that populates C:C with the desired numeric data, so future date tabs are populated with #N/A

...corrected #N/A by adding ISNA to C:C formula (display as 0 until data is inserted...how would I instead modify formula at top to correct for the #N/A?