UPDATE It has been 2 hours. There is still mixed reporting. According to Reuters, Qatar said Iran had agreed to the ceasefire. The ceasefire has not been confirmed or denied by Iran or Israel. Iran and Israel are still both attacking. Trump's post said that the ceasefire must begin within 6 hours, that would be midnight eastern time.
~~In my own personal judgement, I can not definitively say whether the ceasefire is real or fake.~~
https://www.reuters.com/world/middle-east/trump-announces-israel-iran-ceasefire-2025-06-23/
UPDATE 2 It has been 3 hours since Trump's posts.
Fars News reports that "The ceasefire proposal put forward by U.S. President Donald Trump is completely false and was floated to distract public attention from the recent humiliation suffered by the United States following attacks on its bases in the region." Fars News Agency is managed by the IRGC, therefore I consider it to be reliable on reporting decisions of the Iranian government.
https://xcancel.com/DropSiteNews/status/1937308597467132090#m
Iran Foreign Minister Seyed Abbas Araghchi says that there is no ceasefire agreement. "As of now, there is NO 'agreement' on any ceasefire or cessation of military operations. However, provided that the Israeli regime stops its illegal aggression against the Iranian people no later than 4 am Tehran time, we have no intention to continue our response afterwards."
https://xcancel.com/DropSiteNews/status/1937313778451763487#m
The long-term damages will be more relevant for Israel as a sizable portion of their population is now going to wonder if they have enough of a spine to squat on other's land when the other side starts shooting back in earnest. The average Israeli wasn't alive for the last time Israel was in a peer war and has never dealt with a real military raining ordinance down on their heads, and a tremendous number of them have multiple passports and can leave whenever. Iran doesn't have that problem.