Board Thread:The Quarters - Q & A/@comment-24548070-20140215075807/@comment-24150802-20140531191138

Strictly speaking, the XP cap has been in the code for a long time, but it's started to be mentioned in the Tavern and wiki only relatively recently.

When the code is working out how much XP and GP to give you for completing a to-do, if the to-do's value is less than  -47.27, then the code behaves as if the value was exactly -47.27. A to-do will reach that value when it's about a month old, so there's no point to procrastinating for more than a month. :)