Thanks For the info, In case anyone else is interested here's what I've used :
select (( to_number(trunc(END DATE,'D') - trunc(START DATE +6, 'D')))/ 7*5) +
mod(7 - to_number(to_char(START DATE, 'D')),6) +
least(to_number(to_char(END DATE, 'D')) - 2,5) from TABLE NAME
Substitute START DATE...