On most Windows systems, you can right-click anywhere on the desktop, click on "Properties," then click on the "Screen Saver" tab at the top of the dialog box. From there, you can disable your screensaver or adjust the settings so it will not come on for the duration that you choose. 

For most Mac systems, go to the Apple icon and click "System Preferences." Under "Hardware," click "Energy Saver." Then set the computer and display to sleep after whatever duration you prefer, or choose "Never."

For mobile devices, you can adjust your device’s sleep time in “Settings”.