Nice plugin I like it. I have few ideas for features:
1) The option to set or disable the country/countries in admin so the plugin will on display only one location e.g UK. Or selected locations e.g UK, FR & DE. Or hide the country option completely from the booking form.
2) The option to embed the form in a page rather than as a pop-up.
3) The option to send out email reminders for bookings at chosen intervals. E.g 72, 48, 24, 12 etc hours before the booking.
4) The option to change the duration of the countdown timer e.g 5, 10, 15, 20 minutes etc. Or completely disable it.
5) The option to pay a deposit for specific requests via Paypal and issue a receipt. E.g. large group reservations etc.