TheEvilDM
First Post
At my table I would not allow it. I'd allow them to pick the start of an action as a trigger, but since they have not yet begun to take their action, only get ready to take one, they don't suddenly become hasted and able to go before someone else who has already started.
Actually, at least in the case of spells, they have all but completed their action:
PHB pg. 193 said:When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs.
You're obviously still free to rule it either way, but at the very least your assumption that they have not yet begun to take their action is wrong by RAW.