it really depends on your hard drive (read/write) speed, and the size of your database. Also your CPU/Memory speed plays a role.
For example a 30GB (30,000 MB) database, on an average SSD speed would be ~150MB/s R/W speed hard drive would take about 200 sec.
If you have HDD, the speed is way slower, and can takes x 5-10 times more.
I've been asking for a back up progress indicator for a long time. My back ups take ages - more than 30 minutes so far and the whole time it says 'Backup Database (not responding)' so I never really know if it's working and can't use SB during the back up.