Assuming you're asking about the annual meeting of the parish council (and not the annual parish meeting which is something different) the rule in the Local Government Act 1972 is:
7 (2) In a year which is a year of ordinary elections of parish councillors, the annual meeting of a parish council shall be held on, or within fourteen days after, the day on which the councillors elected at that election take office, and in any other year the annual meeting shall be held on such day in May as the parish council may determine.
So it would be unlawful to move the parish council annual meeting into April.
(The parish meeting of a parish shall assemble annually on some day between 1st March and 1st June, both inclusive, in every year. This is not a council meeting, but a general meeting of the parish.)