The length of a fling depends from person to person. It might be as short as 2 days, a weekend, or vacation, or as long as a couple of weeks or months… but not long enough to be a year. It's not even long enough to call it a short-term relationship that usually lasts for 2 years. On the other hand, casual flings can be as long as 3 months. In the end it all comes down to how each of you feels comfortable in the arrangement, your sexual compatibility, how you work around your schedules to meet your desires, and similar things.