When a group wins an invoice it seem that it is based on the time of the first bid or when the bid group was created. The first bid in the group is not necessarily the winning bid. The winning bid could be the any of the subsequent bids that reached the goal sale price.
In the example below the bid which won the invoice was placed at 06:054:05 am, it just so happens that that was the last bid of the group that was placed. That is the time in which the invoice was won.
When a group wins an invoice it seem that it is based on the time of the first bid or when the bid group was created. The first bid in the group is not necessarily the winning bid. The winning bid could be the any of the subsequent bids that reached the goal sale price.
In the example below the bid which won the invoice was placed at 06:054:05 am, it just so happens that that was the last bid of the group that was placed. That is the time in which the invoice was won.
https://user-images.githubusercontent.com/31194353/37261963-0a3c8724-25db-11e8-91c9-69c8e64ce4c7.png