=35-(HOUR(IF(A1<>MIN($A$1:$A$999),A1-MIN($A$1:$A$999),0))*3600+MINUTE(IF(A1<>MIN($A$1:$A$999),A1-MIN($A$1:$A$999),0))*60+SECOND(IF(A1<>MIN($A$1:$A$999),A1-MIN($A$1:$A$999),0)))*0.5