Ask Goigle when Civil Twilight ends in the town you are visiting. In my town, Sunset is at 8:16 PM today. Civil Twilight ends at 8:48 PM. I would want until 8:48 PM today. In Cleveland, OH today, the two times are 8:48 PM and 9:21 PM.
Civil twilight is when the sun provides enough natural light for most outdoor activities without artificial lights. So, after Civil Twilight ends, there would be no excuse for Sonic not to have turned on their lights yet. The Sonic closest to me closes at 10 PM. The farther west a location is in a time zone, the later sunset and the end of Civil Twilight will be in the summer. The two times for Minot, ND today are 9:32 and 10:08 PM, but the Sonic in Minot, ND is open until Midnight, so it will be dark there for the most of the last 2 hours they are open.
Shopping South Jersey, Southeast Pennsylvania, and Delaware above the canal since 2008