The date and time on Google Nexus 7 is by default set to automatic. Listed below are the steps required for manually setting the date and time on your Nexus device.
Step 1: Launch the Settings screen on Google Nexus 7.
Step 2 : In the Setting screen, tap the Date and Time option under System section.
Step 3: un mark the check box with label as Automatic date & time.
This should enable the Set date and Set time option.
Step 4: Tap the Set date option and choose the preferred date.
Step 5: Similarly to set the desired time on Google Nexus 7, tap the Set time option.