First off, I totally agree with BamaVol's three rules - I think it sums it up nicely.

Additionally, though, there can be a variety of definitions of lingering. I grew up in a family where lingering meant more than about 90 seconds after the bill was paid. I married into a family where relaxing and talking and enjoying after-meal beverages for a half hour or 45 minutes post-bill-payment is normal and not considered lingering. (Though I think both sets of families would agree that three hours is more malingering than lingering...)

Sometimes, it's not just geography that determines culture when it comes to dining!