Chrono has two games, both are based around time travel from the start, both probably have loopholes due to it but despite all that I think Chrono is a bit like Doctor Who - an exception to the rule because it doesn't take itself too seriously and, as mentioned, are based around time travel from the start rather than suddenly introducing it later on in a way that causes people to go "BUT IT DOESN'T MAKE SENSE". I haven't played both games, though, so it's hard for me to comment fully on the Chrono series.