New Car Break-in Period

I'm buying a 2018 Toyota Camry SE in a few days, and I have a question about the break-in procedure. In the owner's manual it states the following:

-- Breaking in your new Toyota --
To extend the life of the vehicle, observing the following precautions is recommended:
● For the first 186 miles (300 km):
Avoid sudden stops.
● For the first 621 miles (1000 km):
• Do not drive at extremely high speeds.
• Avoid sudden acceleration.
• Do not drive continuously in low gears.
• Do not drive at a constant speed for extended periods.

This might sound like a dumb question but... what exactly constitutes an "extended period"?
One minute?
Five minutes?
Ten minutes?

I have no problem with letting up on the gas pedal after a pre-determined time period, in order to keep the speed variable and make sure I'm not driving at a constant speed. I'd just like to know what that time period should be.

Any advice would be greatly appreciated. Thanks.