Why does canelé batter have to be made 24 hours in advance? I am experimenting with making canelé. All recipes I've found call for the batter to be made and left in the refrigerator for at least 24 hours before baking, but none say why. 

One guess is that maybe the batter needs to reach a certain temperature get the right consistency while baking (caramelized exterior and moist interior). But I don't think that it would need anywhere close to 24 hours to reach the fridge temperature.

Does anyone know the reasoning or the origin of the 24 hour time, or if it really makes a difference between leaving them in for, say, 6 hours?
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.