Every time a start session is called using Flurry SDK, a new session is registered unless the call was made within 20 seconds [for the same user] of the previous call, in which case these consequent sessions simply extend the existing one.
For Google Analytics, it is different. Google Analytics will group hits (any analytics API call you make is considered a hit in Google analytics) that are received within 30 minutes of one another [for the same user] into the same session.