Could have been done a couple of ways. 7124-7127 are the extension numbers of the voice mail ports, so those are the only ones assigned to group 770.
The "normal" way of providing delayed auto attendant answering is to assign the lines to an empty calling group (other than 770), and have that group overflow to 770. Then you make a mailbox with an extension number that matches that calling group that points to the auto attendant. If you do a "print" of the calling groups, you may find the group that does this, then you remove the lines (or pools, if they are in pools) from that "delayed call handling group", and just reassign them to group 770.
It could also be that your Operator extension's mailbox is pointed to the auto attendant instead of being a regular mailbox that answers and takes messages. In this senario, delete the auto attendant mailbox, remove the extension from the voice mail cover group, and add the lines/pools to group 770.
You could also add Night Service to the Operator extension and send the lines to the auto attendant that way, but that would also put the auto attendant in the night mode unless you also modified the AA's schedule settings.