Joining a dating site has a fair number of pros and cons associated with it. You can meet a lot of really interesting and cool people on such sites, but there is a pretty good chance that you would also get rather exhausted by parading yourself around and getting only mixed results. Sooner or later you might want to call it quits and get out while you are still ahead, and there is also a little thing known as the sunk cost fallacy that you should consider keeping in mind.
The truth of the situation is that the length of time that you should stay on a dating site has a lot to do with how much success you have seen so far. If you keep getting matches, you might as well stick around as long as you are enjoying yourself. However, in the event that you find someone that might be a life partner or if you stop getting matches, it might be time for you to stop your search. This is because of the fact that you would only get upset by your lack of matches, so you should check here to figure out how long is too long.
One way to look at this is by seeing how the site makes you feel. The fact of the matter is that most people get sick and tired of dating sites after having been on them for a year, and the vast majority find partners in half that time. Anyone that has been active on a dating site for this long should think about finding alternative means of social mixing, perhaps in a physical space.