I don't think that's right mate depends on what airline you fly with, if you have a 60 day visa and you return flight is with the same airline for 90 days there could be some problems if you don't have a onward ticket
beautiful country and very clean, shit me up a bit when I had to get on the cable car to Ba NA hill, the wife didn't tell me that part until we were in front of it,
If you coming for 3 months on a 60 day visa, get a cheap onward ticket, airline might stop you from boarding, if your return flight runs over the 60 day visa.