They are actually not allowed to stamp your passport.
When I entered on a FP, they stamped the FP with the date that I entered. I was under the impression that when entering for the first time, it was essential to get the entry stamp.
Platinum, keep the tickets and boarding pass and if there is noone at the airport (try asking around when you arrive) then you should be able to send it with the tickets to the BIA.
As far as six months to apply for the residence card, it's 6 months from the date of issue.
" The U.K. authorities expect long-term visitors and those coming to the U.K. to study or work to have U.K. immigration stamp their passports upon entry into the country. Those who enter the U.K. via the Republic of Ireland and who therefore do not have their passports stamped by the U.K. immigration authorities encounter serious problems once here as they cannot legally work or acquire a local national insurance (social security) number without this stamp. The problem is exacerbated by the fact that U.K. immigration does not have a public access office in Northern Ireland.
We therefore advise all American citizen students and long-term visitors traveling to Northern Ireland who do not have a British visa or entry clearance to travel to Northern Ireland via Great Britain and not via the Republic of Ireland. Travelers who fly into an airport in Great Britain clear U.K. immigration, receive entry stamps in their passports, and therefore enter the country legally. They need no further documentation.
Students and long-term visitors who do not have a British visa or entry clearance and who travel to Northern Ireland via the Republic of Ireland must mail their passports with the appropriate application form to U.K. Immigration authorities to receive an immigration stamp authorizing them to stay in the U.K. For information on the application process, a copy of the application form, information on the current turnaround times and costs, please refer to the U.K. Immigration & Nationality website. "
That's on the US Consulate, Belfast site. I know it says specifically Northern Ireland, but it would be applicable for travel to anwhere in the UK from ROI.
