Consider two cases of people sending messages to each other:
Case 1: Two people are online and both are free. They are doing nothing other than chatting with each other, so both of them are replying within a few seconds. After chatting for some time they go away for the whole day.
Case 2: Person 1 messaged Person 2. Routinely Person 2 checked his messages, saw a message from person 1, and then replied to it. And this process keeps repeating all day. So each other is replying after anywhere from a few minutes to a few hours of getting message, at his convenience.
How can I differentiate between these cases? How can I say I like case 1 instead of case 2? Are there some words that can I use instead of typing this long description?