The clock at each stop
First message to reply: 10 to 15 minutes, whatever the hour. Reply to confirmation: as long as it takes to send three details, often only a few minutes. Confirmation to her knock: about an hour across most of W2, Bayswater and Edgware Road, more in the evening rush or out towards Heathrow, with the exact time posted in the chat. Dinner dates and overnights run more smoothly with a few hours of notice, and a Heathrow hotel needs three hours booked with travel counted in.