Two guests keep arriving after dinner is ready. Can I serve the others before they get here?

At 7:10, the tart was on the table and four guests were waiting. My cousin texted, "Leaving now." She lives half an hour away. Her partner added that they'd eaten a late lunch anyway.

I'd invited everyone for seven and said we'd eat shortly afterwards. We waited, then the early guests rushed through dessert because one had a train to catch. My cousin thanked me for being flexible. I didn't feel flexible; I felt as if I'd made six people's evening follow two people's timetable.

This has happened at the last two dinners. I don't need military punctuality, but I want to mean it when I tell the next group we'll eat at a particular time. Is it reasonable to say we'll start and they can join us when they arrive? I expect she'll hear that as us deliberately excluding her.