The Prologue holds seven main quests and ten side quests. The main quests carry you out of Laslea Glen and into the thirty days. The ten side quests do not survive that transition. Every one of them is missable.
Why this catches people
Openings train you to move. The game has just told you your family will be sacrificed in a month, the map is about to open, and the natural instinct is to get on with it. That instinct costs you ten quests you cannot go back for.
It also costs you the wrong kind of time. Prologue side content is the cheapest content in the game to complete, because you have not yet started spending days against a deadline that matters.
One to watch specifically
A Mother's Plea is both hidden and time sensitive. It is not simply a quest you might skip; it is one you can fail to find at all. If you are the kind of player who wants every thread, slow down before the Prologue closes.
The general rule for the rest of the run
Once the valley opens, watch for the hourglass icon on a quest objective. That marks a time-sensitive objective, and it is the game telling you, plainly, that this one will not wait.