As of May 4th, 2018, community events are active again. As of this date, the event is at 50/78 and the Cologne Games Week 2018 is the current one so it looks like they are the same events like last year, just updated from 2017 to 2018 and I believe they will update at the same time they use to (5 PM, PDT) Here's a list (I'm American so I apologize for the way we write out dates and apologize for the dates I'm writing when they become available. These are dates when they will be available for my time zone which is the Pacific time zone)
(Event #)(Date)(Event Name)
Event 50 - 4/29 - Cologne Games Week 2018
Event 51 - 5/6 - Formula A in Belgium 2018
Event 52 - 5/13 - Formula A in Italy 2018
Event 53 - 5/20 - Clio Cup Challenge 2018
Event 54 - 5/27 - The Green Hell 2018
Event 55 - 6/3 - American Prototype Power 2018
Event 56 - 6/10 - Radical Raceway 2018
Event 57 - 6/17 - Big In Japan 2018
Event 58 - 6/24 - Pagani Passion 2018
Event 59 - 7/1 - DTM Masters 2018
Event 60 - 7/8 - Group A Challenge 2018
Event 61 - 7/15 - New York Minute 2018
Event 62 - 7/22 - Palmer Sport Track Day 2018
Event 63 - 7/29 - Push the Button 2018
Event 64 - 8/5 - Brno Bimmer Hot Lap 2018
Event 65 - 8/12 - Dual in the Desert 2018
Event 66 - 8/19 - Formula Catalan 2018
Event 67 - 8/26 - Supercars of Silverstone 2018
Event 68 - 9/2 - The Emporer's Festive Bonanza 2018 (II)
Event 69 - 9/9 - New Year, New Racing (II)
Event 70 - 9/16 - Racing Resolution (II) (This is an event from the projectcarsgame.com/on-demand)
Event 71 - 9/23 - Winter Sun (II)
Event 72 - 9/30 - RUF and Ready (II)
Event 73 - 10/7 - Sonoma Showdown (II)
Event 74 - 10/14 - Big Trouble in Little China (II)
Event 75 - 10/21 - Highway to Hell (II)
Event 76 - 10/28 - Spring Cleaning (II)
Event 77 - 11/4 - American Le Mans (II)
Event 78 - 11/11 - The Final Parade Lap (II)
So that's 29 events that you have and need to post a time in 20 of these. If starting from 0, the latest you want to start these is July 1st. To be safe, I would start June 24 which is the week before. The reason I would start there is because of Event #70. I'm not sure if this is some sort of DLC race or not but if someone could comment and let me know, I will update the solution.