How long should i roast a REALLY small beef joint for?

[girlafraid]

It's only 650g and I'd like it to be medium rare. Normally do the Jamie Oliver pre heat to 240C and then adjust to 200C when putting joint in for about an hour

I think that would be too long???

I would do it at the high temp for 20 minutes and then 20 minutes on the lower.

Rest with foil for another 20 mins.

thanks so much