It would help if you thought about this in terms of how we describe things: i.e. we describe
an object by defining an extent in 3D space. Similarly, if we described a length of time to describe it, we would just be describing a duration. That's exactly what you're doing when you ask, "how long is the movie?" With a event it is relatively simple: 'such and such occurred for so long.' With an object it is a little strange, we don't necessarily know how long an object will exist, or how long it has existed.
It comes in handy in particle physics though.
That's more of a philosophical question---how you interpret these things.... but yes, thats definitely accurate to some extent.
No. Not at all. Photons can't 'see' anything---because they don't have a valid reference frame. Additionally, even if they could 'see,' they would no equivalent of actions---because everything would appear to be at the same instant in time and space.... sounds weird because it doesn't work--you can't think in the photons frame.