If you do not want to book the ticket, I recommend...

If you do not want to book the ticket, I recommend to go no later than 9.30 and no earlier than 16.00 in order to avoid long waits and spend only 8 against the 12 of the one booked online and for a limited number.
I just queued for 15 minutes ... the tour is not long and there is no crowd to see the David.