takes 7 hours avg, chk with lowest priced dealer. they must drop lower front suspension, big job, for access to oil pan. expect to pay 1200.00-1400.00 for the job to be done correctly. dealerships hand the proper tools and training.
while your at it do the valve cover gasket, and have them check the fuel housing gasket.
if you do all the above you will not have any oil leaks for quite sometime.
own a 330i 2001 since new, great car just due the maintenance as required