Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The timing is not so critical.
The important thing is to be consistent. So whenever is the best time for you, schedule it then.
There may be minor benefits to dosing at certain times, but if trying to follow such a schedule is going to result in missed doses and irregular dosing, then do not bother.
A stable schedule is better than an optimum schedule; there is not that much benefit to dosing at certain times.
Light can break down certain forms of fertilizer (Chelated minerals). If you can dose these in the evening then they tend to last longer, be available to the plants longer.
Excel breaks down, too, but is best used by the plants in the daytime, so AM dosing seems to be best.
Repeat: These are such minor benefits that a regular schedule will be more important.