In Japanese culture, politeness is highly valued, and there are several ways to politely decline a request or express that you don't have time for something. Here are a few common phrases:
すみません、今はちょっと時間がありません。(Sumimasen, ima wa chotto jikan ga arimasen.) Translation: "I'm sorry, but I don't have time right now."
申し訳ありませんが、今は他の用事があります。(Moushiwake arimasen ga, ima wa hoka no youji ga arimasu.) Translation: "I apologize, but I have other prior engagements at the moment."
大変申し訳ございませんが、今はお手伝いできません。(Taihen moushiwake gozaimasen ga, ima wa otetsudai dekimasen.) Translation: "I sincerely apologize, but I'm unable to help right now."
今は残念ながら都合がつきません。(Ima wa zannen nagara tsugimasen.) Translation: "Unfortunately, I can't make it at this time."
Remember to use polite speech forms (keigo) when addressing others, such as adding -ます (masu) to the verb endings and using respectful language. Additionally, expressing regret or apologizing before declining is considered courteous in Japanese culture.