Well ive been in portugal for like 10 days, got a tan, im naturaly olive skinned as it is, and ive gone a tint darker, was wondering how long the tan will last until i get my natural skin colour back?....

For me, any tan that darkens my skin that much lasts for months.  When I was a child, I'd often have a week or two in the sun on summer vacation, plenty of it spent in a bathing suit (where I lived, it was rarely warm enough for outdoor swimming and there was no place to do it, so that was only on vacation)--and the outline of the bathing suit straps would be visible on my skin til around Christmas.  When I spent a couple weeks of that vacation with relatives in Florida, my skin turned about a shade darker, and it took at least six months to get pale again.