I kind of feel for Saul here, Lord knows I probably would have done something like he did. Saul had good reason fuss, Samuel was late, the army was leaving and there was a horde of Philistines waiting to pounce - at least this is what it sounds like. Regardless, Saul should have waited. It is always better to wait on the Lord than jump ship before it reaches dock.
I am one of those with the worst timing, really I have the worst timing. Good ideas, but just a minute too late or a day to early. The times that things have worked out for me, is when I waited on the Lord rather than pushing myself or others to make a decision or do something rash and ill-timed. So really the question here is - well, when do I know whether it is time to wait on the Lord or just make the decision? That is a good question you ask; I likely don't have the best answer, but I do suspect that if any of your answers in a circumstance can be answered by let's just wait on the Lord. Then maybe it is a good thing to consider, likely then maybe we don't know what the best is and then waiting on the Lord for clarity and resolution is the proper answer. The Lord will give us the best in due season.
When in doubt, wait on the Lord.