Depends on your needs and starting point – it might take from a few hours to a few weeks to run the whole thing. The best way is to start with a WordPress hotel theme, but make sure that it has a one-click demo import feature (all vacation rental themes by MotoPress have this option). Later, you have to substitute all the dummy data with your own content, provide detailed info for each accommodation you rent out, and create custom booking rules if you want to have one.