How long does it take to travel from Bangalore to Hampi?

There's several buses that leave from Majestic to go to Hampi, they look to all take around 7.5 hours or longer. If you drove yourself then it could be shorter at around 6.5.

There is one sleeper bus I can see that leaves at 10pm and gets in before 6am, this could be a good choice as you would be able to travel throughout the night and still get a full day there, also saving you a night of hotel costs.

There's an overnight sleeper train that goes to Hospet, Hampi is further 30min local bus/taxi ride from there though. This leaves at 10pm and arrives at 8am.

This link also seems useful in explaining the lack of direct flights and trains, as well as providing some alternative buses to those you already mentioned.

This is the expected time, it takes 6 hours and 30 minutes to drive there according to Google, a bus takes around 7 hours 30 minutes.

You can read train and bus options here.

I might be a little late into this.

A lot of buses / trains go till Hosapete from Bangalore. You can easily find a bus to Hampi from Hosapete in the morning. They are more frequent too and it takes less than an hour in the morning. The best option is to travel overnight in a sleeper class bus. You can book tickets using https://ksrtc.in/oprs-web/ which is run by the state government.

The travel time by bus takes 7 to 8 hours by bus. Make sure you reach Hosapete not after 5AM in the morning. Otherwise you might have to wait a while to catch first bus to Hampi.

You board your bus from Majestic. However there are other pickup points available along the route within the city. Again, refer to https://ksrtc.in for pickup points.

Another option is to reach Hosapete by train. You can refer to IRCTC website for bookings. The station code is HPT. Cost wise, buses are more expensive than sleeper class is train and less expensive compared to 3AC coaches in train.