How long do I have to have a home before I can refinance?

I've had my home for 6 mos through the VA, but I will be getting stationed in another state soon. My ex wife and child will still be living in it, and I will pay the mortgage payment as a form of child support. My interest rate is only 6%, But I want to refinance for a interest only fixed rate loan for like 5 yrs, and will sell the house when the housing market recovers. I owe 61k on it and its appraised at 90k. Also what would be the approxiamate closing costs for a loan of that amount?