Why is there a time limit on discovering alien life?
If a NASA chief believes that aliens will be discovered by 2025, that is her opinion. So what? It neither confirms nor refutes the existence of alien life. It's one person's opinion.
What evidence discovered by human probes discounts the idea of alien life elsewhere in the universe?
Why are you so fixated on grouping scientists into either atheist scientists or creation scientists?
You clearly don't get it and thus have no credibility. This is sad for one because there are many weak-minded people like you who believe in fake science and fairy tales. It is sad and pathetic and at the same time laughable

due to lack of perspicacity.
There is a time limit because aliens have been long overdue and NASA head honcho has claimed it.
For one, you do not understand the fine tuning facts. Even the atheist scientists understand it and have moved on to multiverses as the explanation. The trouble is there is no observational data or experiment to base their beliefs on.
There is no evidence of aliens whatsoever from the probes. The groups and people who do have credibility in this field -- Enrico Fermi, Frank Drake, SETI, Elon Musk and more have said intelligent aliens would have contacted us already. Also, we would have found a microbe or some basic type of life elsewhere. There have been more than enough probes sent out as I have stated. Thus, you do not understand the Drake equation and Fermi paradox and what it means. This has been explained to you in the past and yet you continue to ask and repeat the same boring questions.
Even after this, the intelligent people like myself and the creation scientists are subjected to ramblings by the leftist head of NASA that due to their superior technology aliens will be found. The technology is paid for by out tax dollars, that they will find a microbe and more. It's based on false hope such as water on Mars and false science. Thus, it's better to spend our money on something better like better space stations and to see if we can set up a supply station for them on the moon. Maybe we can set up a defense system there to prevent large asteroids from hitting our planet.
Finally, to answer your last question, it's the creation scientists who are left out. These are the people with the real observational science that there are no aliens. Why not believe them and spend our tax dollars on real science projects.