Shouldn't take any longer than 25 minutes either.
Make sure you keep that thin stuff away from your rover! I use 15-40 and I live in Iowa.

 

Put in Mystic - 15w/50 or 20w/50 from the autoparts store.
You get it in a big 4 to 5 quart jug.

Or Rotella - truck oil 20w/50. That will get you home probably.
10w/30 Synthetic is great for a nice shiny new BMW.
But, not for these old engines which are really loose.

Your VIN on your 2003 may be in the OIL PUMP problem range.
Or, you may have had a rod knocking from low oil pressure.

I would put in that thick oil first - as you are on the "oil pressure line"
of iffy at best with that 10w/30 thin as water oil in there now.

I just drove 1551 miles in my 2001 Discovery II. On pins and needles.
As per Savanna's advice - I drove it 65mph and no faster.
I would do the same.
Just go slow with thick oil.
Of course - the best way is not to drive it at all and get it fixed.

I am always one to get it back to "home base" and get it fixed when you are of clear head and not in "trip mode".

 

interesting.

my D1 might spontaneously combust should I drive it 65 mph for an extended period of time.

 

Thats why I only drive 60. lol

 

I use 15w-40 in the summer and 5w-40 in thew winter.
These engines love to be revved and worked hard once and awhile.
I rev mine to 5,000+rpm at least once a year, usually when climbing steep sandy hills.
T-case locked in lo, trans in 2nd, go pedal mashed to the wood.