Does it make any difference if I transfer my CPF OA to SA in Dec 2021 VS January 2022?

The difference is when you start earning 4% SA interests. For OA to SA transfer, you would start earning SA interests on the month of transfer, therefore transferring in Dec 2021 would give you an extra month of interests (1.5% interest delta between OA and SA).

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Transferring from OA to SA gives you an additional 1.5% interest rates.