Some questions I can choose Most Helpful after an hour of asking, but others it says it's too soon. I posted a question yesterday and I tried picking Most Helpful but it said too soon for Most Helpful. Today I posted a question, and I was able to pick Most Helpful after two hours.
To pick a MHO quickly, a minimum of 4 opinions is needed. If you get 4 opinions in a short amount of time (2 minutes or so), the system will allow you to select. Otherwise, the system makes you wait a day or two in the hopes that you'll receive more responses.
Now this is a very good question I think the algorythym may be set to a minimum of 10 replies have to be recorded before the MHO can be given. Just a guess on my part? There are (Gagger's) on here all the time maybe one of them will see your post and can answer your question.