BRRR strategy- refinance asap or let it ride?

[Stephen Hundley]

I bought a house using a unsecured loan from a local bank that's 6% interest only. My monthly payments while I rehab is only about $300/m. It's going to rent for $1,350/m. Once I put long term financing on it my note will be around $900 all in. The bank will give me up to a year before I have to refinance. 

My question is, once it's rented, would you stay on the interest only for the rest of the year and build cash flow or refinance on long term financing immediately?