(Need Advice) Rowing from Manhattan to Montreal in 8x

I'm part of a men's club that has been constructing our own Octuple Scull for the past ~7 months or so. It is seaworthy, and we're planning on launching on July 1st. However, I have my brother's July 4th party I want to be back in NYC for. How long could we estimate it would take to go there and back?