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What matters is the number of working days. If PIP starts on working day 1 then the credit hits your account on working day 4. Monday and Tuesday were bank holidays, so you count like this:
Day 1: Friday 23rd December (PIP appeared for UK EFT)
Day 2: Wednesday 28th
Day 3: Thursday 29th
Day 4: Friday 30th (Money hits account today)
The money has, indeed, hit our account today. However, depending on the way your bank works (ie if they report as at close of the previous day), you may not see today's credit in your online banking system until tomorrow or Monday.