Please see the calendar next to the tour itinerary page. You will notice 3 colours; Green, White and Gray.
The green signifies "Instant Availability" which means you can select these dates and book instantly without waiting for the confirmation.
The white signifies "Availability upon Request" which means can select these dates and ask if the local expert is available on that date.
The grey signifies "Unavailability" which means it is impossible to go on the tour on these dates.
To get a quick booking done, simply look out for green dates! This way, you will book directly without waiting for the confirmation.