I think, U should never resign unless and until it is obvious you are gonna lose ( losing queen doesn't mean that)..Also if he/she is low on time then never ever do that 
.. Time is a crucial part of game..
There are 30% chances your opponent can blunder if its some timepressure thing..
Lost queen at move 51 and still won on time
Yeah lol exactly XD.. Nice!
I would say that if you are continuing the game because you see chances to get back into the game, then it is reasonable. However, if someone is continuing to delay the game out of frustation, then it is bad ettiquette because it is just wasting time for no benefit
It depends on how you are losing. If you are playing vs someone with a considerably higher rating who has outplayed you throughout and achieved a position where you can clearly see how they will finish you off, be polite, resign and offer your congratulations. It's poor etiquette to fire off random moves s quickly as possible in a hopelessly lost position in desperate hope of time forfeit. But if you think you have chances to come back and are seriously playing to pull out a better result, or don't see that you are certainly lost, play on. Even if you are pretty certain you are lost, continue and see if your opponent knows how to cash in: if he does you may learn useful techniques, if he doesn't he really can't complain.
It is best not to resign as a beginner. You might become more resourceful. Sometimes you will get a draw or even a win out of lost positions.
If you are interested, in this article you might see what exactly do I mean:
https://www.chess.com/blog/nklristic/swindling-my-way-to-victory-first-steps-to-chess-improvement
Some stronger players can make the swindling artistic. I am of course pretty weak and my tricks are more in line with my low level chess. 
if I were coaching you I would put it this way..
you should not be playing fast chess yet, because early on you need to take your time and think. Your games should be at least 30 min long (15/ side) or more. Playing longer games, resign when you have lost if there is a lot of time left on the clock. If there are 2-3 min left total (both sides), finish up if you see a chance to win or even draw it. Experience will tell you when you have lost and should tip the king, you will learn that with playing. Playing to win on time by stalling is legit, but as a beginner, in a longer game, don't do this for 10 min after screwing up your opening. If the other guy is low on time, a couple of min left or less, sure. Use common sense and common courtesy -- do you want to play someone who drags a game out for 20 min or more for no reason?
also, if your opponent has mate next move or two, let him mate. Later you can resign at this point, but it gives new people a thrill to finish on the board.
As a beginner, the only time you should resign is when you have pawns and your opponent has pieces, and there isn't a way to promote your pawns. Mainly for your own sanity, because often times your opponent will promote rather than just use their remaining pieces to win.
You shouldn't resign if you are winning in position and or on time. Also note that if you are in a winning position keep fighting with the pieces you are going to use and ignore pieces you aren't. For instance if you aren't going to be using a rook and it takes the opponent three moves to take your rook, that means three free moves for your attack.
On the topic of not resigning, I recently had a game where I was down 8 points of material, and won some of it back slowly. The game ended when the opponent blundered his queen and resigned. Not resigning sometimes can be a good idea.
As a beginner (<800 rating), I do not resign games. There is always the chance my (also beginner) opponent may blunder material or time, and if not, I can learn from their tactics.
I also appreciate when others don't resign as it forces me to "seal the deal" and find checkmate. When my opponent does resign early, I typically use the "Finish against Computer" button and force myself to find the win.
But is this the case when beginners play too?
I am a beginner, playing with other beginners, and I feel there is benefit in trying to actually achieve check mate.
I played a beginner a few days ago and stupidly lost my queen early on. He had a better position, and more material. He should have check matted me at move 20. Yet he was chasing me around until move 40something. I though it was great practice from for me and the other player, learning how to properly handle our pieces.
What do chess teachers recommend to their young students and what is your opinion?