The traditional period in the northern hemisphere for the Week of Prayer for Christian Unity is 18-25 January. Those dates were proposed in 1908 by Paul Wattson to cover the days between the feasts of St Peter and St Paul, and therefore have a symbolic significance.
In the southern hemisphere where January is a vacation time churches celebrate the Week of Prayer around Pentecost (suggested by the Faith and Order movement in 1926), which is also a symbolic date for the unity of the Church. In Aotearoa New Zealand the Week of Prayer is celebrated between Ascension Sunday and Pentecost Sunday, which in 2022 is between Sunday 29 May and Sunday 5 June.