IOS – Setting the default calendar in iOS

You can enter events to specific calendars by holding down the + button

See here the entry from iCal help:

Add events to a calendar

You can add any kind of event to your iCal calendars. For example, you can add meetings, doctor appointments, and family activities. You can’t add events to a calendar you subscribed to.

1. Open iCal
2. Click Add (+) at the top of the iCal window or press Command (⌘)-N.
   Events are added automatically to your default calendar.
   If you want to choose a different calendar for the event, hold down the Add button (+), and then choose a calendar.
3. To change your default calendar, choose iCal > Preferences, click General, and then select a calendar from the Default Calendar pop-up menu.

Settings > Mail, contacts, calendars > Default alert times > birthdays

Apparently there are a few options here. You cannot specifically set a custom time at the time of my writing this, but it is possible to pick "a day before", "2 days before", "1 week before" or on day of event. I don't see a way to select a different time though other than 9 am.