How long? East coast to Oshkosh

I'm flying from Western Mass to Oshkosh, VFR. I cruise
about 70-75 mph and it's about 900 sm from home to OSH.
Given prevailing wind direction, likelihood of fronts and
afternoon T-storms how many days would you allow for that
trip? I had originally planned 3.5. I d like to be there no
later than Sunday at noon, so I was leaving at dawn on
Thursday. A friend who regularly delivers similar aircraft
over similar distances thinks that's not enough time, and
suggested two extra days (leave Tuesday morn).

Anyone want to comment?