Say the whole thing, not just the greeting.
You send "hi" or "hello" and wait. The other person replies "hey". Then you finally ask your question. Now they have to wait for you to type it out, and you've made a simple exchange take twice as long.
That "hey" to "hey" round trip cost 2 minutes for zero information.
Put the greeting and the question in the same message. That's it.
One message. Instant answer. Everyone wins.
"Hey, quick question - do you know when the report is due?"
Simple. Respectful. Effective.