What do you mean by XC, only leaving the field or actual starting small scale orientation training?
I don't remember exactly when I started NAV training, but first acquaintance with VOR/HSI etc must have been around 20-25 hours into PPL, with dedicated training right before x-country flying myself (does make little sense before, you will forget anyways). Started x-country flying at about 45 hours and passed exam end of 50ies in the hours (all JAR-FCL, so including extensive CVFR). But I have to admit, passing exam was not my goal, learning to fly was, so I did not hurry at anything.