Slow roast pork - please help me work out cooking time

[silver28]

i am making a slow roasted pork recipe that tells me to cook a 5.5kg shoulder joint for 5.5 hours at GM4/180, or instead to use two 1.75kg boneless shoulder joints and reduce cooking time to 4.5 hours

I am using a 2.5kg boneless shoulder joint so planned to cook for about 4 to 4.5 hours, do you think this sounds about right or does anyone know a more scientific way of working out the cooking time?

Thanks in advance.

this is supposed to be a yum recipe and he cooks it for 6 hrs and it's only 2kg.

Thanks loopydo. I did it for about 4 hrs and it was delicious tho not as tender as it could have been so will do for longer on a lower heat next time.