Hello,
Me and my Landy 110 Td5 and another couple in their Toymota did London/Timbuktu/London over March/02, just as the then mandatory convoy going south between Morocco/Western Sahara and Mauritania had finished.
We did the round trip in 5 weeks as it was all the time we could spare. I would suggest this is a bear minimum duration, as it involved 8-12 hours driving per day with very few rest days or time for looking around - very tiring. We planned and prepared carefully to save time...
The main problems are:
1/ Time of year, need to pick time slot between too hot and potential swampy approaching Timbuktu.
2/ Minefields between Western Sahara and Mauritania - know where they are..!
3/ Bandit activity - story then was avoid north and east of Timbuktu, but check to hear latest...
If you haven't already, get yourself the Michelin 953 for route planning.
Basic route is Marrakesh, Agadir, Atlantic coast of Morocco and south to Dahkla - roads to this point are very good but often with slow lorries. South towards border with Mauri. No real road through no man's land (beware mines) to Nouadhibou. Then 2-3 days pure desert and beach (beware tides) driving to Nouakchott. Then roughly east to Nema which is generally good tarmac with some broken up patches, so stay alert.
South over border to Mali and Nara. A lot of grading and improvements here as long as you take the 'newer' western side route. After this you could go south to Bamako or try east to Sokolo, but finding seasonally shifting tracks via the latter is difficult and slow going. If you go down to Bamako (corrugated road to hell) and then head NE, initially the roads are OK, but track finding starts to get difficult.
Not the most scenic of Saharan trips, but gives a great sense of achievement...
Must dash now, but by all means e.mail me james.gj.stephenson@bt.com with any questions that I will try to answer...

Good luck

__________________
Best regards,
James Stephenson
Land Rover Defender 130 camper
www.JamesUK.net