When you use the Snooze function in Gmail, there are three default times which are morning, afternoon, and evening set to 08:00 (8:00 a.m.), 13:00 (1:00 p.m.), and 18:00 (6:00 p.m.), respectively. You can set the snooze time by picking the date and time manually. The default settings are actually managed in Google Keep. Here are the steps for how to change the default snooze times.
Step 1: Login Google account and open Google Keep.
Step 2: Click the Gear icon in the top right corner.
Step 3: Select Settings.
Step 4: change the Reminder Defaults to the default snooze times you want.
Step 5: Click Save.
Step 6: Return to Gmail and click the Snooze button (clock icon), the default times should now be reflected as those you selected.
Note: To see all snoozed email, click Snoozed label at the left sidebar.