Why does canelé batter have to be made 24 hours in advance?
I am pretty sure it is for cross-linking to form gluten and possibly rearrangements of other proteins also. As far as I can work out, there is no impact to either caramelisation or maillard. Resting time and temperature do need fine tuning for different sizes though which is quite logical and may explain different recipe timing. So, do look out for that. Temperature plays a part in the reaction kinetics. Again, not looked into it, but chilling suggests better to slow things down and possibly to prevent unintended fermentation. 5C from experience is perhaps the upper limit.