How might this effect your coaster travels in IN? Well...
Holiday World is going to remain on Central/Chicago time all year round. They will be on the same time all throughout the year as you Illinois & Wisconsin folks. However, despite wanting to be in the Central/Chicago time zone, Indiana Beach's county was denied that request and will be on Easter/Ohio time all year round. Unfortunately, this means one less hour of playing in the dark at IB. This also means Indy will be 1 hour ahead as well, of course.
So in summary:
HW: same time zone as Chicago/Wisc people (central)
IB: 1 hour ahead of Chicago/Wisc people (eastern)
Only NW IN & SW IN will be on Central time from now on.
Plan your trips accordingly and don't forget about the time difference and miss the first hour at IB.

For those who want more info, check out http://www.happynews.com/news/1192006/eight-indiana-counties-to-switch-time-zones.htm.