We already answered your ticket (note, a double post support request isn't needed. Ticket OR forum next time please)
...but for those playing along at home, here's the answer again.
Hello!
1) No, the early bird discount applies automatically based on the date... and nothing else.
2) Yes, each discount code has an OPTIONAL date/time setup. You can set the date/time when it becomes active AND when it expires.
3) You control calculations. First, in the admin listing of events, there is a column with a link "Fee Ordering". Click this and you can drag-n-drop all fee/discount items related to the event. This is important when using % calculations as when the % applies does matter. So you can order things to how you want them to work.
Also, make sure to check the bottom of the first tab of configuration as you can set all discount/fee items (early bird, late fee, member discount, etc) to how they are used in a group registration. Set if the fee/discount is applied once for the group or to each member separately.