Is it possible to change the default time for notification for the mobile push notifications?
At this time its not possible to change this.
In that case is it possible to turn this off?
Head into settings, top right gear icon. Then under Reminders, there is a Default Reminder option that can be turned off.
Really? Because my Android has this setting: Settings -> Notifications -> Reminders -> Default time. Is this not what you are looking for?