What is the position with saying selichos (end of Elul and Aseres Ymei Teshuva) with a minyan that starts straight after maariv at say 10:30 or 11pm?
Most of the poskim said you can't say slichot before midnight. Harav Moshe Feinstein said that it's possible in she'at hadchak - if it's very very hard to say them after midnight.
You can see more details in Hebrew here.
For more discussion, including a proper interpretation of Igros Moshe, see:
Besides nicely summarizing R. Moshe's view (which I corrected in a comment to the answer above), he also quotes the view of R. Ovadya that perhaps if one cannot say it past midnight, it should be said instead before mincha.
And here: When is the proper time to say selichos?
R. Willig expresses a preference for reciting them after mincha if after midnight is not possible.
Rav Ovadia says that not only is it forbidden, but if you find yourself in a place that is doing it, it is forbidden to say amen and you should leave the place, especially if they want to count on you for the minian.