Q for those using Ar of thickeners

Can Ar formulas be made up in advance of time or can they only be made up when needed, the reason i ask is that my son drinks more than the 100 made up and less than the 150 so if i switch to Ar formula is there going to be alot of wastage which i want to avoid as formulas can be expensive. Are both the Ar formulas and normal formula with adding a food thickener the same consistency or are they completely different
Any info people can give wuld be great, thanks in advance