If you are earning a minimum of 38 euro per week from your part time job you will be entitled to get one class A contribution per week.
If you ceased this part time employment you can then make voluntary contributions up to age 70. This would cost you 500 euro per year. You can start voluntary contributions from immediately after you cease employment. There is no necessity to wail until the start of the next calendar year.
Currently you could claim a pro rata pension at age 66.
If you do this you can no longer gain any extra Prsi contributions.
You need to calculate how much pro rata pension you would gain at age 66 compared to the pension you will achieve after you reach 520 contributions to see if this is worthwhile.
Calculate the cost of voluntary contributions + the loss of pro rata pension from age 66, in order to see how many years it will take you to break even.
Include pre entry and change of status credits in your calculations.
Also include the mix of Total contributions and Yearly average contributions ratio for the year you will reach the 520 contributions level.