There is no amount of time that guarantees you won't interfere with another user on a shared channel without time division. Any protocol used has to account for it no matter what.

But discussion of that is irrelevant because the regulation is no more than one every 30 seconds and each one can't be longer than 1 second in duration. This necessarily limits the length of messages you can send or requires more efficient modulation and/or weaker error correction at the tradeoff of worse weak-signal performance.