Did British Empire and Vietnam exist in the same era?

Yes, the two civilizations both existed around 1945 CE.

Which lasted longer, British Empire or Vietnam?

British Empire lasted longer (414 years).

British Empire: Avrupa; Vietnam: Asya

British Empire (1583 CE – 1997 CE) and Vietnam (1945 CE – present) lived in the same era.

The empire with the most extensive territory in history. It was referred to as "the empire on which the sun never sets."

Socialist Republic of Vietnam · Asia

Did British Empire and Vietnam exist in the same era?: Yes, the two civilizations both existed around 1945 CE.
Which lasted longer, British Empire or Vietnam?: British Empire lasted longer (414 years).
Which regions did British Empire and Vietnam rule?: British Empire: Avrupa; Vietnam: Asya