Phrase 'that once would have been two days hence'

[KLPNO]

Hi everyone
I'd like to ask a question that I cannot understand in the following passage:

Tapping her earpiece, Annabella linked to her aunt and uncle. She usually had dinner with them once a week, and that once would have been two days hence. It would have been nice to do it more often, but her schedule barely allowed for the once.

What does 'that once would have been two days hence mean?'

[Conchita]

It means that she was due to have dinner with them two days from then.

[KLPNO]

Thank you very much, Conchita.