I am normally fairly hesitant concerning time-travel movies because it is next to impossible to get them right. They more or less always become very unrealistic and full of paradoxes. I would almost go as far as to say that producers making serious (non-comedy) time travel movies are the ones that are scientifically too stupid to realise that it is just going to be a mess, or they do not really care about the issues hoping that the audience also will not care.
This movie is really proof of this. It is full of paradoxes and annoying “but if this happened now then that couldn’t have happened t... read the rest.