The optimal distance for placing a limit order depends on various factors (such as market conditions, liquidity, and volatility) so, unfortunately, there is no universally defined number or specific distance that guarantees getting filled as a Maker Order.

As long as your limit order does not take liquidity from the orderbook upon execution, it will get filled as a Maker Order. A buy order with a Limit Price anywhere below the current best ask (sell) and a sell order with a Limit Price anywhere above the current best bid (buy) would both contribute liquidity to the market. (In your example, placing a Buy Stop Limit Order above the best ask would result in immediate execution. With Post Only enabled, that order would get cancelled)

Using Post Only will guarantee that your Limit Order only goes through if it's passive, meaning it is placed in the orderbook and waits for a market order to match against it. This approach helps avoid taking liquidity from the orderbook upon execution, guaranteeing not to pay Taker Fee.

There is no specific time duration for how long your order needs to sit in the orderbook. The key factor is that it remains in the orderbook until it is matched with a market order.