即时 is common in tech contexts: 即时通讯 (instant messaging), 即时翻译 (real-time translation). For everyday 'immediately,' 马上 or 立刻 are more natural. Compare 及时 (timely/in time) - different character, different meaning.
mistakes
Don't confuse 即时 (instant/real-time) with 及时 (timely/in time). They sound identical but 即 means 'immediate' while 及 means 'to reach/in time for.'
