Sorry for this late response Tim,
Yes, crystals can only be moved to and from the chest at the end of each day, between rounds.
Just to expand on the original question, am I right in saying that crystals cannot be moved to the treasure chest until a day's mining is complete (i.e. at the end of a round). Players can't move crystals into their treasure chest mid-day but have to wait until a day's end, right?