Once you finished your meal and washed mayim achronim you need to bentch immediately. Do not eat or drink anymore. Do not talk even a little divray Torah. Do not delay even the time it takes to walk 22 amos and certainly do not do any activities. (ShA1 – MB1 – ShaH3)
If you need to interrupt between mayim achronim and Birkas Hamazon for an urgent matter, or b'dieved you interrupted – wash mayim achronim a second time. (MB1)
“Let’s bentch” terminates the beracha rishona. If you want to drink, say a new beracha first. Don’t eat anymore because there’s an argument if you need to say a new beracha for more food or not. (ShA1 – MB9)
When you rely on someone for your meal, you may suggest “Let’s bentch” but it will not terminate the beracha. However, if you make a firm decision not to eat or drink anymore even with the baal habayis, you will need to say another beracha if you change your mind. (ShA2 – MB10)
If the baal habayis says “Let’s bentch” then the meal is terminated for everyone. Only if you specifically had in mind to continue eating and drinking can you exclude yourself. When you proceed to eat, it’s best to inform everyone else of your exclusive intentions. (ShA – MB11)
Lifting a cup of wine to bentch also constitutes a termination of the meal just like mayim achronim. (ShA3 – MB13)
A guest’s beracha on fruit, covers all of the fruit that the baal habayis will serve. Even if the guest assumes that they won’t bring anymore, that thought does not terminate his beracha. He knows it’s all dependent upon the will of the baal habayis; not is own. (ShA5 – MB17)