There is little question that selichos is best said after Chatzos (midnight). Many have the custom to say it right after chatzos on the first night of selichos before Rosh Hashanah. There is however a practice for some shuls
(you know who you are) to daven selichos at 9 or 10 PM and the question becomes is this permissible? According to Rav Ovadia you are basically wasting your time. According to Rav Moshe his view is a bit more lenient and perhaps this is where the minhag comes from. The Shulchan Oruch clearly states it's not ais rotzon and that is the main issue. Read more about this by clicking here.