What is the special day mentioned in the novel Mission to Kala?

The special day was the day the Chief's new wife would be brought to his home by her tribe.

The Chief had just married another wife - his seventh, as far as I can remember - and he had been in a fine state of anxiety for weeks, wondering what day his tribal in-laws would choose to deliver his bride on the doorstep. The tribe in question carefully concealed the day they had selected : they wanted to give the Chief a surprise. Warning of the event depends on how well off the bridegroom is. A man of slight means has to be notified in advance, so that he can make special preparations for these highly important days of celebration. What use was there, they argued, in notifying so substantial a man of property as the Chief? What extra preparations would he need to make? He had everything at his beck and call the whole time.