The garage door opener lights are set to turn off minutes following the door's closure so that you'll have the time to walk with safety. They're usually set around 4-4 ½ minutes and you can change it. Also, there are safety lights, which are on for as long as you keep the door open.
It's the easy way to make your life comfortable. What will happen if you return home and there's no power? Why go through the trouble of leaving the car outside to get inside and open the door manually? Backup batteries give electric openers autonomy for about fifty cycles and you'll still be protected from safety risks.