it is not a job that takes that long because the 300tdi doesnt need the water pump to be removed as with other landies .
if youre belt doesnt wear then you can go up to 40,000 miles between changes but in reality id not let it go for much over 20,000 miles judging by my own experience of timing belt wear rates in my 300tdi .
the inherent problem with 300tdis is that the timing belt itself walks forward off the injector pump gear if the pump gear isnt aligned properly and no amount of lipped crank and idler pulleys will stop this from happening . in fact its only the timing cover that keeps the belt on the gear in a lot of cases .
whatever you do , make sure you do have the belt changed as soon as possible .
the updates landrover advised belt tension is 9ft/lbs and thats what i set mine to .
i have changed my belt at 12,000 mile intervals , ie once per year ,after all it takes me only a few hours to do a belt change , what cost of a timing belt at 20 odd quid compared to an engine blown and in pieces .