Lunch break?
 

I scanned the rule book/competition manual to no avail. Is the minimum one hour lunch break an unspoken, unofficial deal?

Yes. But even if the TD indicates you'll have an hour after the last group is in when giving announcements in the player meeting, they can change their mind due to extenuating circumstances.

FWIW, a couple tournaments I played this year gave an hour from the second to last card coming in for lunch, that way the one really slow group didn't make everybody finish in the dark.

one hour lunch break indeed

Clever.

As far as I call as well, there is nothing in the rule book about it. Would surprise me if there was too.

So it is something that you can probably count on, but shouldn't. :)

Stinks if you're on the last card--the one that's been slowed down all round by the second to last card.

Nope, because in that case those two groups will come in at about the same time and both will get an hour. It only makes a difference when a single card is slow and the td was able to give them enough of a cushion that it didn't affect other cards too much.