Your best clue for that is multi fold. Check the last few years almanac records for your area. Also study the archives for Indiana Tapping on this site. You might also check another surrounding state but look for areas with weather close to yours.
Guessing starting dates is tricky at best. What I do is try to have things ready to go and watch the 5 day and 10 day weather forecasts, when that looks right start tapping. If you are just starting out my guess is that you can tap everything in an hour or 2, that makes you quite flexible. Producers with thousands of taps often start tapping a few weeks before the expected season, but that is not an option unless you are on tubing and a tight system.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.