This is how I manage it now ..which is bit heavy!
=IF(DAY(EOMONTH(Timesheet!$N$4,0))=31,SUM(COUNTIF($N7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($O7,{"A","UV","PV","R","TR"}))++SUM(COUNTIF($P7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Q7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($R7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($S7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($T7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($U7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($V7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($W7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($X7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Y7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Z7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AA7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AB7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AC7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AD7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AE7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AF7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AG7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AH7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AI7,{"A","UV","PV","R","TR"}))++SUM(COUNTIF($AJ7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AK7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AL7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AM7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AN7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AO7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AP7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AQ7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AR7,{"A","UV","PV","R","TR"})),IF(DAY(EOMONTH(Timesheet!$N$4,0))=30,SUM(COUNTIF($N7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($O7,{"A","UV","PV","R","TR"}))++SUM(COUNTIF($P7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Q7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($R7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($S7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($T7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($U7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($V7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($W7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($X7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Y7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Z7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AA7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AB7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AC7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AD7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AE7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AF7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AG7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AH7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AI7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AJ7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AK7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AL7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AM7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AN7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AO7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AP7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AQ7,{"A","UV","PV","R","TR"})),SUM(COUNTIF($N7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($O7,{"A","UV","PV","R","TR"}))++SUM(COUNTIF($P7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Q7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($R7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($S7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($T7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($U7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($V7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($W7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($X7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Y7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($Z7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AA7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AB7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AC7,
{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AD7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AE7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AF7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AG7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AH7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AI7,
{"A","UV","PV","R","TR"}))++SUM(COUNTIF($AJ7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AK7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AL7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AM7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AN7,{"A","UV","PV","R","TR"}))+SUM(COUNTIF($AO7,
{"A","UV","PV","R","TR"}))))