Is Flixbus allowed to rebook a trip at its own discretion?

My trip from Berlin to Poznan was just changed from 3:30 a.m. to 9:25 a.m. without my consent, and now I can only rebook for an additional €10 or lose €7 if I cancel. A colleague has the same trip with a departure point in Bochum. His departure is 170 minutes late, and he can rebook for free or continue on his current trip.

Is this all legal? Are they allowed to make this decision for me, and why wasn't I given a choice about rebooking? I feel a little ripped off.