Turn that question back around at ATC. When they issue an instruction, they give the pilot what, maybe 5 seconds before they repeat it?
Many controllers get PO'd WAY faster than that. There are a few who don't allow anytime for anyone else to speak either. On the other hand it doesn't take many pilots not listening to jam a frequencey up.
Same thing....if the controller doesn't respond to me within 5 seconds or so, I'm going to assume they didn't hear my original transmission for some reason.
Another thing that no one seems to do is use standard phraseology on check-ins.
I always check in just like this (yes, I want a cookie):
"Atlanta Center, Airliner Twelve Thirty-Four, level, flight level three-seven-zero"
I've seen ATC videos that request that pilots say "level", "climbing" or "descending" before they say the altitude. I try to do that just to help ATC out a bit. I do sound a little stupid saying level almost twice in a row there, but I'm not the only one who uses this phraseology. For lack of anything better, I guess it's the ATC-preferred standard.
This bit is interesting to me. The AIM wants us to say "climing to FL XXX' Personally I think this is bad technique. "To" and "for" sound just like "two" and "four". In a congested environment this can get ugly (and be hard to say). Personlly, I never say "to" or "for" on the radio.
Another thing, why doesn't everyone announce vacating one assigned altitude for another (aka descending to cross an arrival fix at the assigned altitude)?
This is another one that should go back to ATC. Whenever I decide to follow the AIM and do this, ATC seems annoyed at my extraneous call. I've never heard them chew someone out for not making it.
One last question, what's the proper way to pronounce a flight number such as 3001, 2006, etc? Three-Thousand One? Thirty Oh-One? Thirty Zero One? Three Zero Zero One?
My understanding is that your callsign is the one thing you get some authority over, whateve you checkin with is what they should use. I always say it the way that seems easiest.
I actually had a controller once who wouldn't accept my acknowledgements unless I responded with Thirty Zero One instead of Three Thousand One.