As a junior line holder on the 756 sub base (flying both the 757 and 767) you will get 6 trips to Europe and 12 days off for quite a while. When you are senior enough to hold FO or IRO (International Relief Officer) on trips worth 16 or more hours you will get 5 trips or 15 or 16 days off a month. I would guess at a minimum a year or two (depending on growth and retirements) to hold 15 or 16 days off a month.
You will only hold 757 and not 767 on a regular basis until you are at least above the 40% in the base. That may take two or more years.
Hope this helps.
EWR 756 Captain