From the main menu, select Endurance and make sure that you turn aiming aids off. It doesn't matter what difficulty you play on, you can still unlock this, and the other endurance achievements. So go for Easy, which mainly only affects the speed of which balls drop on your table.
The aim of endurance mode is to pot balls quicker than new ones appear on your table. You want to only really go for balls that are either near pockets or lined up straight with the cue ball and the pocket. If there is nothing on, try setting up your next pot, rather than going for long hopeful shots that hardly ever come off.
Every so often you will get a 'Ball Stop Dropper' to use. This will appear on the bottom right of the screen saying push
to use. As indicated, this stops balls appearing on your screen for 15 seconds. You can elect to save this for when your getting close to your limit of 24 on the table, however please note that you don't build up your next ball stopper until you have used your current one.
If you reach 20 minutes at the Endurance table you will also unlock all the following achievements:
For a total of 170GS! Happy Potting!