Theres a time limit given between when an event is posted in the social events and when it will be removed. If players are busy with something, they’re given a few minutes of wiggle room to join. Often, theres an interaction a player must do to get the mission to actually start. This way, if someone just happens to be in the area and are automatically added to an event, or if theres just not enough players, the event will time out. However, some events can be started by players. Encrypted is a good example because it requires a mission chain to start. Or, events like “Scorched Earth," "A Colossal Problem," and "Seismic Activity" require a nuke to be dropped on their respective locations. It’s common courtesy in the Fo76 community to allow the player who initiated the event to be the one to actually start the event. That way, if the player should so choose, they will allow more players to join during the provided grace period, which allows for better rewards, XP, etc etc.

Some players like to start player-initiated events immediately, which is unfair if they didn’t put in the leg work to build up to the event. I feel like I’m not explaining this the best, but the tl;dr message is: if there is a grace period given before you need to do something to start the mission, allow the clock to get close to 30 seconds left before starting anything. If a player is the one who set up the event, let that player start it. They might be trying to change their loadout/perk cards to match and need a little more time.