The test opening and closing time is the time period for which the test is active and can be taken up by candidates. Outside this time frame the test cannot be taken up.
This is how it can be done:
Step 1: Log into the CG account
Step 2: Click on Manage Tests on the menu bar
Step 3: Click on Test Hosted and select Edit next to the concerned test
Step 4: Click on Settings on the Side Bar and select Test Settings.