Does hamotzi need to be recited again if a meal is interrupted and resumed later?

Let's suppose one recites hamotzi, eats some bread, has a few bites of the meal, and then is interrupted by some matter. Some time later, one returns to the table to resume the meal.

Is it necessary to recite hamotzi again? My hunch is that the answer depends on how much time has elapsed during the interruption: if several hours have passed, then one might argue that one is actually beginning a "new" meal, requiring new brachot, but if only a few minutes have passed, that would not be necessary. Is that hunch correct?

The general question of "When does a meal 'expire'?" seems related to the question of how long one has to recite birkat hamazon, but in that context the relevant fact is whether one is still full. In the scenario I describe, one has not yet eaten enough to be sated. (Also please note that I am not asking about an interruption between reciting hamotzi and eating the bread.)

To clarify: The question is not about reciting birkat hamazon. It is about whether one needs to recite hamotzi again on returning to a meal that had been interrupted.

Edit: Per Jay's answer, it seems that the critical factor is not the duration of the interruption, but rather the nature of the interruption, i.e. what exactly the person does during that interval. So in order to sharpen the question, here are some of the kinds of interruptions that I am wondering about. Are there any general principles that would help one distinguish which of these would require a new hamotzi?

1. Taking a phone call



2. Chatting with a neighbor at one's own front door


3. Chatting with a neighbor who comes to the front door, and is then invited in to sit in the living room


4. Chatting with a neighbor at the neighbor's own house


5. Getting more food from the fridge or oven


6. Picking vegetables or fruit from the garden, to add to the meal in progress


7. Getting a bandage for an accidental cut (either for oneself, or for someone else at the table)


8. Using the restroom


9. Being called away to complete a minyan at another location

Some of these involve a "change in location", but others (e.g. #5) do so only nominally.

Answer

Most Poskim hold that the hamotzi bracha remains in effect indefinitely, unless there is some interruption (such as intentional napping). See Mishna Brurah 184 s.k. 17. So it would seem that length of time is not a factor, and in your case one need not make a new bracha regardless of how much time has passed.

Regarding the new examples you've added - the Rema writes in O.C. 178:7 that 'divrei rshus' such as going to the bathroom or dozing off do not constitute an interruption. The Levush (quoted in note 41 of the Kaf Hachaim) explains the Rema as follows [translation mine]: "The general principle is, anything that a person does occasionally in middle of doing other things is considered minor and is not considered hesech hadaat".

If, however, there was a change of location (i.e. one left the building) and the eating session ends vis-a-vis birkat hamazon (i.e. one is no longer hungry), then it appears that one would need to recite a new hamotzi - see Mishna Brurah 184 s.k. 10.