Not quick at all It could happen even when you talk on the phone with the person the first time before you even see them

Whether you call it "crush" or "transference" makes no difference. It's all about the mechanics of the process, not the labels. It's just when people prefer to think of it as just a "crush" it allows them to think that it "just happens" for no reason, which, in my experience, is never the case. But it's much easier to think of it just as a crush, because, in that case, no self-reflection is needed. If it's a crush then it is something that is happening TO me, as opposed to something I AM CREATING.