You know that the question is somewhat stupid and that it is hard to explain it.
But anyway, let's have some fun
I'll use some numbers to explain my idea:
Dembele vs Malcom vs let's say Sandro
Dembele:
1. best young player at French ligue 1,1
2. very good in Dortmund
3. overally rated as one of world's best talents by many journos, coaches, fans
Let's say that these things have earned him "20 credits/coins" for Barca's career.
If he'll play like a crap on training grounds, he will lose 5-10 coins and have only 10 coins/chances left.
He will get a certain amount of matches.
If in a match he'll play well, he'll earn extra coin.
If he'll play bad, he will lose 1 coin.
If he will play average/ok, he will stay on the same number of coins.
So:
15 coins before a match
1) if you play well, you will earn a coin=15+1=16 coins now left
2) if you play bad, you will lose a coin=15-1=14 coins left
3) if you play average/ok, you will stay on the same level=15 coins still left
So, let's say that Dembele had 20 coins when he came here.
He lost 5 coins with some training problems, injuries, not stretching, eating unhealthy.
But still had 15-ish coins/chances left.
He played a few bad games, and dropped to 10 coins left.
But he had some good games (Juve).
Over time he dropped to 5 coins in spring 2018'.
But in the end of a season, he played better and stayed on 5-10 coins.
So, he still had some chances left for a 2nd season, even though a board considered selling him during summer due to his drop of coins from 20 when he was signed to 5 coins at the end of a season.
In this season, he started well, and improved his number of coins, to let's say 15.
But in the last few matches, he played bad and dropped to 10 again.
If he'll play that way in the next Months, he will first get benched and then the board will consider selling him again.
If he'll start to play well, he will earn enough of coins and jump to 20-30 and he won't be sold and he will continue to play this coin-game in the 3rd season.
Now, Malcom:
1. he was not as good as Dembele in 2 countries
2. he is considered as a lesser talent in general
So, Dembele started with 20 coins.
Malcom, due to his lower potential, will start right away with only 10 coins/chances.
Let's say that he had 2 bad cameos till now, and his number of coins already dropped to 7-8.
Also, if he is bad (on skills) on training grounds, that will further lose some coins/chances from his Barca's career.
But anyway, let's assume that he still has 7-8 coins left...
If he'll play meh in matches when he'll get a chance, he will soon drop to 0 coins: he won't get new chances after that and the board will consider selling him in summer.
If he'll start to play good in the next matches, he will improve his coins-tally and buy more time to stay at Barca and show his worth.
For the end, Sandro Ramirez while he was here.
In general, way weaker potential than Dembele and Sandro.
And not too impressive in former teams like Dembele.
Dembele earned 20 starting coins due to his potential and previous history in other clubs.
Malcom earned 10 starting coins.
Sandro will earn only 6 coins.
And now, a player like Dembele can play 10-15 bad matches BUT he will still get some chances, since he started with a high number of credits/coins.
Some average talent like Sandro will get way fewer amount of chances.
And if he doesn't grab his chance right away (and improve his number of coins), he will soon run out of coins (6 matches) and he will hardly get new chances after that.
So, there is no answer: HOW MUCH time would you give to all players.
Imo, this is roughly how it works at Barca (without coins, of course, haha).
In short:
1. a player with a higher potential on paper will get more chances to prove himself.
And even if he'll suck in the beginning, he will get some amount of 2nd chances.
2. a player of a lower overal potential and of average history in Bteam or in other clubs, will get lower amount of chances to prove his worth.
And for him it will usually be: it's now or never from the game 1.
He will get 3-10 matches max in his Barca's career and that's it.
Unless he grabs a chance right away, he will be loaned or sold.
And a loan and some crazy perfrormances in a new club will be his last chance.
If he will be good on a loan, he may get back (Deulofeu) and earn 10 coins again.
But if he'll play bad again (after a loan spell), like Deulofeu, he will again lose all his coins and he will be sold for good this time.