[Delmobile]

You're still at Bertram's Hotel, aren't you? It's a gentle joke: "Greenwich Mean Time" is of course the official, undisputable standard for time-keepers. Her (guardian, isn't he?) feels a little uneasy about Elvira drinking alcohol, but reminds himself that she must be aware of the correct way to behave socially. It's also a reference to time, in that "times have changed" and now young women can be seen in public drinking cocktails without damaging their reputation. So, "Greenwich social time" might be considered the official, undisputable standard for arbiters of society.

[not a teacher]