When do pending transactions post to my account?

It depends. The timing depends on the scenario.

Pending means, this money is currently on hold for a deposit or a payment. That's why they're shown separately.

While they're pending, this money isn't included in your available balance, which shows only what you have available to spend right now.

Once the transaction has processed, it will move from Pending to your transaction history, and your balances will update.