There is no concept of average sex time or anything like that. Sex consists of many things. Sex is not limited to intercourse alone.  It also consists of things like cuddling, kissing, giving oral pleasure to each other etc. It is called foreplay. Time of foreplay can vary from one hour to many days. Even preparing food together, spending an evening together can be a part of foreplay. So rather than counting time, focus on the happiness and satisfaction. It will make your and your partner’s life much happy.