The oxbow website says: Mix 3 Tbsp per kg of body weight daily.
So an average bunny would need around 7-8 tablespoons, bear in mind this is the dry product, it's more once it's mixed up. You'll need to feed it in several sessions every few hours, as it is important that the stomach does not become empty. You'll also need to syringe water, as bunnies with slow/stopped guts are at risk of dehydration.
If he'll eat it willingly from a bowl or spoon, do this, as it will be less stressful. You can also offer him normal pellets, softened with water to make them easier to eat, and lots of his favourite hays. Try and keep his favourite foods around him to tempt him to eat - fragrant herbs like basil and mint are good choices because the smell makes them irresistible to bunnies.
Is your bunny also on pain relief (metacam) and gut stimulants (pro-kinetics like emeprid and zantac)? These are essential in keeping everything moving whilst he's not eating properly. If not, please take him back tomorrow morning (most vets are open for a few hours on Saturdays) and ask for some.
If he stops eating completely, it is then considered an emergency and he'll need to be hospitalised, so keep a close eye on him. I hope he's feeling better soon.