Translation:This reminds me that it is time to return to the ship.
I can see both sides of this argument. While "that reminds me" is by far more commonly what you would hear, "this reminds me" is the correct translation and could apply to something specific and near at hand, for which "that" would not apply. eg "This [timetable] reminds me..." So DL is right not to accept "that". Having said that, "That reminds me" is borderline idiomatic because we often use it for things that are specific and near at hand and should technically be described by "this". To further complicate matters Spanish speakers learning English should be aware that we often use "this" for things that are in the present, but "that" for things that are in the past. So, if somebody mentions something that reminds us, we generally do not say "this reminds me" even though the conversation is ongoing, but instead "that reminds me" because what they have said is in the immediate past. Man, I could go on all day, but I won't.