The phrase "a lengthy post" is correct and usable in written English.
You can use it to describe a written piece that is long in length, often referring to articles, blog entries, or social media updates.
Example: "After reading a lengthy post about climate change, I felt more informed about the issue."
Alternatives: "an extensive article" or "a long entry".
In a lengthy post on Facebook, Zuckerberg expanded on his vision for Oculus.
Ferdinand even wrote a lengthy post on Facebook asking what is meant when we say 'world class'.
Stacey Williams shared a photo of herself, alongside a lengthy post explaining the emotions she currently experiences in her job.
In a lengthy post on Instagram, Questlove, described the way in which Phife and the group "wrote my destiny".
To toast the occasion, Mr. Zuckerberg wrote a lengthy post on his personal Facebook page, calling the transaction an "important milestone" for the company.
Jason Nious, a fellow performer who was almost paralysed working on the same show in 2009, wrote of his grief in a lengthy post on Facebook.
Budget wrangling delayed filming until June 2014, filming wrapped in October that year, before a lengthy post-production period.
At the end of a lengthy post-D.U.I. class, in which "they basically teach you how to get out of a D.U.I., which is great after the fact," Ms. Handler had to tell her arrest story to the group.
In a lengthy posting on his Facebook page, Mr. Brophy explained his change of heart, saying that children who are not here legally still had the right to an education.
Get ready for yet another wearable… Neyya, a Bluetooth ring designed for remote-controlling other mobile devices, is finally launching today after a lengthy post-crowdfunding delay and a substantial rethink of the original concept.
Ra.One was initially scheduled to release on 3 June 2011, but delays due to a lengthy post-production process and escalating costs pushed back the release date.
