do you have to wait to sundown to light the menorah?

Yes. The best time to light is about half an hour after sundown. This way, all opinions of when to light are fulfilled.

The exception to this is Friday night, when Shabbos begins before sundown. One first lights the menorah, making sure there is enough oil/wax to burn for at least half an hour AFTER NIGHTFALL (in the USA this is 45 minutes after sundown, meaning the menorah should burn at least an hour).

When to Light:

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The menorah should preferably be lit immediately at nightfall. It is best to wait, however, until all the members of the household are present. This adds to the family atmosphere and also maximizes the mitzvah of "publicizing the miracle."

*The menorah can still be lit (with the blessings) late into the night, as long as people are still awake.*

The menorah should remain lit for at least 30 minutes after nightfall, during which time no use should be made of its light.

yes. Light it after sundown. But, if you can't do it so early it is OK to light it even late at night.