Do I need to book moorings in advance in Croatia in peak season?

[syperk]

First time charterer here... We have a boat booked from Rogoznica for the second week in August this year and are planning on visiting some of the islands to the south (e.g. Hvar, maybe Vis).

Being entirely new to this process, is it necessary to reserve moorings in advance? If so, how far in advance? Is the day before usually OK? Or should I be booking things weeks out and gambling on cooperative winds? I'm assuming we'll mostly be using mooring buoy fields. Is my-sea.com a good site to use for this? Thanks!