I think that one time should be okay in most cases! But if you decide not many people answered and it got pushed deep into the depths of the internet I would at least wait awhile before you ask it again. Maybe even reflect on whatever answers you've gotten and try some of that advice first, that way your question might even be a little different. I know that people will become frustrated if they see the same question worded the same way by the same person several times in the same month! So I wouldn't do it unless you feel it's totally necessary, and once again, if you do, make sure you wait a fair amount of time before posting it again.