The ten sit, as it is written: and “in the assembly of the elders they will give thanks to God”, and the one who blesses stands because this blessing is instead of the thanksgiving sacrifice and the person who gives the sacrifice stands and sacrifices. And therefore we do not say Birkat HaGomel at night, but rather during the day. And retrospectively if someone blessed at night they fulfilled their duty – and see the Hatam Sofer Orakh Hayyim Siman 51.