Help with GREP find and replace

I have never used GREP before, and am stumped.  I have a document that lists the times for many different classes.  The times are variously listed as 9-10, 9- 10, 9 -10, or 9 - 10, for examples.  The problem is that there may be no space or one space on either the left or the right sides of the hyphen.  I want all the times to appear as 10:30 - 11:30, for example.  That is, the hyphen should have one space on either side of it.  I think this could be accomplished with GREP find and replace, but I don't understand the syntax well enough to make it work.

Can someone tell me how to write the find and replace expressions?  (Of course the actual times could be any hours).

Thanks!