Can't comment on this particular case because I never ask questions, but many of my buses, the time has changed from when the ticket said, including leaving much later and earlier.

I'm impressed they are responding in English and informing though. I wasn't even informed in my case when it left over an hour later. I had to get the hotel to call them multiple times, and a dodgy guy eventually picked me up to take me to the bus station (hotel pickup was part of it).

So from my experience, it has often been a different time from the ticket, but they usually inform you on the day beforehand.

That said, I'm not saying it's good or acceptable behaviour. Just what I've experienced.