If its a 3.0 with an M40 box, like mine, its about 8hours for a professionally equipped garage that does gearboxes and clutches on these sort of vans. A place by me charges £300 to do gearbox swaps for me.. theyre normally done within a day. Apparantly they drop the subframe, because its a nightmare to get the box out.
A freind and i tried to do it on the drive and it took us 21 hours with axle stands on large blocks - all done over a long weekend. it is a VERY heavy gearbox, very awkward too. I wont do that again, i would rather pay a garage £300-500
If you drop the box, and you have a concentric clutch slave- put a new genuine one in, dont do my mistake as youll have to pay again when it leaks, and it will.( based on two failing on two gearbox swaps).. the second slave cylinder failed with only 20,000 miles on it, as the gearbox swap must have disturbed it.