Time travel is probably one of the most tricky conceits for any movie. The moment you decide your movie will involve time travel, you are immediately faced with the unavoidable fact that you can’t write such a story without creating a paradox.
How can the Terminator possibly succeed at killing John Connor since he already hasn’t?
If you are going to tell a good story about time travel, you have to embrace the paradox. You have to just accept that it doesn’t all make sense but if time travel were really possible, it wouldn’t all make sense.
If they can go back to the exact point in time they want to get some whales, why couldn’t they come back five days earlier so they wouldn’t be crippled by the probe?